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The Genus Pinus
by George Russell Shaw
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THE GENUS PINUS

PUBLICATIONS OF THE ARNOLD ARBORETUM No. 5



THE

GENUS PINUS

BY

GEORGE RUSSELL SHAW



Es giebt jedoch auch Arten—und dieses ist fuer den Systematiker wie fuer den Physiologen gleich wichtig—welche sich den wechselnden Bedingungen der Feuchtigkeit so vollkommen anpassen, dass ihre extremen Formen zu ungleichen Arten zu gehoeren scheinen.

Schimper.

CAMBRIDGE PRINTED AT THE RIVERSIDE PRESS 1914

REPRINTED 1958 BY THE MURRAY PRINTING COMPANY FORGE VILLAGE, MASSACHUSETTS



CONTENTS

Page Plate

PART 1 CHARACTERS OF THE GENUS 1

Cotyledon, Primary Leaf, Bud and Branchlet 1, 2 I

Secondary Leaves 2 II

External Characters 4

Internal Characters 4

Flowers and Conelet 7 III

Cone 8 IV

Phyllotaxis 12 V

Cone-tissues and Seeds 12-16 VI

Wood 17 VII

Bark 18

PART 2 CLASSIFICATION OF THE SPECIES 22

Sections, subsections and groups 25

Section Haploxylon 26

Subsection Cembra 26

Group Cembrae 26

Pinus Koraiensis, Cembra, Albicaulis 26, 27 VIII

Group Flexiles 28

Pinus Flexilis, Armandi 28, 30 IX

Group Strobi 30

Pinus Ayacahuite, Lambertiana 30, 32 X

Parviflora, Peuce, Excelsa 32, 34 XI

Monticola, Strobus 34, 36 XII

Subsection Paracembra 36

Group Cembroides 38

Pinus Cembroides, Pinceana, Nelsonii 38, 40 XIII

Group Gerardianae 40

Pinus Bungeana, Gerardiana 40, 42 XIV

Group Balfourianae 42

Pinus Balfouriana, Aristata 42, 44 XV

Section Diploxylon 44

Subsection Parapinaster 44

Group Leiophyllae 44

Pinus Leiophylla, Lumholtzii 44, 46 XVI

Group Longifoliae 46

Pinus Longifolia, Canariensis 46, 48 XVII

Group Pineae 48

Pinus Pinea 48 XVIII

Subsection Pinaster 50

Group Laricionea 51

Pinus Resinosa, Tropicalis 51, 52 XIX

Massoniana, Densiflora 52 XX

Sylvestris, Montana 54 XXI

Luchuensis, Thunbergii, Nigra 56, 58 XXII

Merkusii, Sinensis, Insularis 58, 60 XXIII

Group Australes 62

Pinus Pseudostrobus 62 XXIV

Montezumae 64 XXV

Ponderosa 66 XXVI

Teocote, Lawsonii 68 XXVII

Occidentalis, Palustris 70 XXVIII

Caribaea 70 XXIX

Taeda, Glabra, Echinata 72, 74 XXX

Group Insignes 76

Pinus Pringlei, Oocarpa 76, 78 XXXI

Halepensis, Pinaster 78, 80 XXXII

Virginiana, Clausa 80 XXXIII

Rigida, Serotina, Pungens 82, 84 XXXIV

Banksiana, Contorta 84 XXXV

Greggii, Patula 86 XXXVI

Muricata, Attenuata, Radiata 86, 88 XXXVII

Group Macrocarpae 90

Pinus Torreyana, Sabiniana 90 XXXVIII

Coulteri 93 XXXIX

INDEX 94



INTRODUCTION

This discussion of the characters of Pinus is an attempt to determine their taxonomic significance and their utility for determining the limits of the species. A systematic arrangement follows, based on the evolution of the cone and seed from the comparatively primitive conditions that appear in Pinus cembra to the specialized cone and peculiar dissemination of Pinus radiata and its associates. This arrangement involves no radical change in existing systems. The new associations in which some of the species appear are the natural result of another point of view.

Experience with Mexican species has led me to believe that a Pine can adapt itself to various climatic conditions and can modify its growth in response to them. Variations in dimensions of leaf or cone, the number of leaves in the fascicle, the presence of pruinose branchlets, etc., which have been thought to imply specific distinctions, are often the evidence of facile adaptability. In fact such variations, in correlation with climatic variation, may argue, not for specific distinction, but for specific identity. The remarkable variation in the species may be attributed partly to this adaptability, partly to a participation, more or less pronounced, in the evolutionary processes that culminate in the serotinous Pines.



PART I

CHARACTERS OF THE GENUS

THE COTYLEDON. Plate I, figs. 1-3.

The upper half of the embryo in Pinus is a cylindrical fascicle of 4 to 15 cotyledons (fig. 1). The cross-section of a cotyledon is, therefore, a triangle whose angles vary with the number composing the fascicle. Sections from fascicles of 10 and of 5 cotyledons are shown in figs. 2 and 3. Apart from this difference cotyledons are much alike. Their number varies and is indeterminate for all species, while any given number is common to so many species that the character is of no value.

THE PRIMARY LEAF. Plate I, figs. 4-6.

Primary leaves follow the cotyledons immediately (fig. 4) and assume the usual functions of foliage for a limited period, varying from one to three years, secondary fascicles appearing here and there in their axils. With the permanent appearance of the secondary leaves the green primaries disappear and their place is taken by bud-scales, which in the spring and summer persist as scarious bracts, each subtending a fascicle of secondary leaves. At this stage the bracts present two important distinctions.

1. The bract-base is non-decurrent, like the leaf-base of Abies fig. 5. 2. The bract-base is decurrent, like the leaf-base of Picea fig. 6.

The two sections of the genus, Haploxylon and Diploxylon, established by Koehne on the single and double fibro-vascular bundle of the leaf, are even more accurately characterized by these two forms of bract-insertion. The difference between them, however, is most obvious on long branchlets with wide intervals between the leaf-fascicles.

The bracts of spring-shoots are the scarious bud-scales of the previous winter; but the bracts of summer-shoots have the form and green color of the primary leaf.

THE BUD. Plate I, figs. 7-11.

The winter-bud is an aggregate of minute buds, each concealed in the axil of a primary leaf converted into a scarious, more or less fimbriate, bud-scale. Buds from which normal growth develops appear only at the nodes of the branches. On uninodal branchlets they form an apical group consisting of a terminal bud with a whorl of subterminal buds about its base. On multinodal branchlets the inner nodes bear lateral buds which may be latent.

Fig. 7 represents a magnified bud of P. resinosa, first immersed in alcohol to dissolve the resin, then deprived of its scales. This bud contains both fascicle-buds, destined for secondary leaves, and larger paler buds at its base. These last are incipient staminate flowers, sufficiently developed for recognition. Such flower-bearing buds are characteristic of the Hard Pines in distinction from the Soft Pines whose staminate flowers cannot be identified in the bud.

The want of complete data leaves the invariability of this distinction in question, but with all species that I have examined, the flowers of Hard Pines are further advanced at the end of the summer. In the following year they open earlier than those of Soft Pines in the same locality. The staminate flowers of some Hard Pines (resinosa, sylvestris, etc.,) are not apparent without removing the bud-scales, but, with most Hard Pines, they form enlargements of the bud (fig. 9).

Invisible or latent buds are present at the nodes and at the apex of dwarf shoots. The former are the origin of the numerous shoots that cover the trunk and branches of P. rigida, leiophylla and a few other species (fig. 10). The latter develop into shoots in the centre of a leaf-fascicle (fig. 11) when the branchlet, bearing the fascicle, has been injured.

The size, color and form of buds, the presence of resin in quantity, etc., assist in the diagnosis of species. Occasionally a peculiar bud, like that of P. palustris, may be recognized at once.

THE BRANCHLET. Plate I, figs. 12-14.

The branchlet, as here understood, is the whole of a season's growth from a single bud, and may consist of a single internode (uninodal, fig. 12-a) or of two or more internodes (multinodal, fig. 13), each internode being defined by a leafless base and a terminal node of buds.

The spring-shoot is uninodal in all Soft Pines and in many Hard Pines, but, in P. taeda and its allies and in species with serotinous cones, it is more or less prevalently multinodal.

The uninodal spring-shoot may remain so throughout the growing season and become a uninodal branchlet. Or a summer-shoot may appear on vigorous branches of any species with the result of converting a uninodal spring-shoot into an imperfect multinodal branchlet. The summer-shoot may be recognized, during growth, by its green, not scarious bracts and, at the end of the season, by the imperfect growth of its wood and foliage (fig. 14).

The perfect multinodal branchlet is formed in the winter-bud (fig. 8-a) and the spring-shoot is multinodal. It is gradually evolved among the Hard Pines, where it may be absent, rare, frequent or prevalent, according to the species. In fact there is, in Pinus, an evolutionary tendency toward multinodal growth, with its beginnings in the summer-shoot and its culmination in the multinodal winter-bud, most prevalent among the serotinous Pines.

The multinodal shoot is never invariable in a species, but is rare, common or prevalent. This condition prevents its employment for grouping species. For Pines are not sharply divided into multinodal and uninodal species, and no exact segregation of them, based on this difference, is possible. In fact the character is unequally developed among closely related species, such as P. palustris and caribaea. Both produce multinodal shoots, but the former so rarely that it should be classed as a uninodal species, while the latter is characteristically multinodal. The multinodal spring-shoot, however, has a certain correlative value in its relation to other evolutionary processes that are obvious in the genus.

The length of the branchlet is much influenced by different soils and climates. In species able to adapt themselves to great changes, the length of the internode may vary from 50 cm. or more to 1 cm. or less. In the latter case the branch is a series of very short leafless joints terminated by a crowded penicillate tuft of leaves (fig. 12-b). Such a growth may be seen on any species (ponderosa, albicaulis, resinosa, etc.) that can survive exposure and poor nourishment.

The presence of wax, as a bloom on the branchlet, is associated with trees in arid localities, especially Mexico, where it is very common. With several species the character is inconstant, apparently dependent on environment, and is a provision against too rapid transpiration.

The branchlet furnishes evidence of the section to which the species belongs, for the bract-bases persist after the bracts have fallen away. The color of the branchlet, its lustre, the presence of minute hairs, etc., are often suggestions for determining species.



THE SECONDARY LEAF. Plate II.

Secondary leaves, the permanent foliage of Pines, are borne on dwarf-shoots in the axils of primary leaves. They form cylindrical fascicles, rarely monophyllous, prevalently of 2, 3 or 5 leaves, occasionally of 4, 6, 7, or 8 leaves. The scales of the fascicle-bud elongate into a basal sheath, deciduous (fig. 15) in all Soft Pines except P. Nelsonii, persistent (fig. 16) in all Hard Pines except P. leiophylla and Lumholtzii. Inasmuch as these three species are easily recognized, the fascicle-sheath is useful for sectional distinctions.

EXTERNAL CHARACTERS.

The number of leaves in the fascicle is virtually constant in most species, the variations being too rare to be worthy of consideration. With some species, however, heteromerous fascicles are normal. The influences that cause this variation are not always apparent (echinata, etc.), but with P. ponderosa, leiophylla, sinensis and others, the number of leaves in the fascicle is, in some degree, dependent on climatic conditions, the smaller number occurring in colder regions. In Mexico, for example, where snow-capped mountains lie on subtropical table-lands and extremes of temperature are in juxtaposition, the conditions are favorable for the production of species with heteromerous fascicles, and the number of leaves in the fascicle possesses often climatic rather than specific significance.

Among conifers, the leaf of Pinus attains extraordinary length with great variation, from 5 cm. or less to 50 cm. or more, the maximum for each species being usually much more than twice the minimum. Climate is the predominating influence; for the shortest leaves occur on alpine and boreal species, the longest leaves on species in or near the tropics.

The length of the leaf is complicated by the peculiarities of individual trees and by pathological influences; as a general rule, however, the length of leaves is less or greater according to unfavorable or favorable conditions of temperature, moisture, soil and exposure. Therefore the dimensions of the leaf may be misleading. It can be said, however, that certain species always produce short leaves, others leaves of medium length, and others very long leaves.

Persistence of the leaf varies with the species and with the individual tree. But it is noteworthy that the longest persistence is associated with short leaves (Balfouriana, albicaulis, montana, etc.).

INTERNAL CHARACTERS.

Since the leaf-fascicle is cylindrical, the cross-section of a leaf is a sector, its proportional part, of a circle. Theoretically the leaf, in section, should indicate the number of leaves composing its fascicle. This is absolutely true for fascicles of two leaves only. No fascicle of five leaves, that I have examined, is equally apportioned among its five members. It may be divided in various ways, one of which is shown in fig. 18, where the leaf (a) might be mistaken for one of a fascicle of 3, and the leaf (b) for one of a fascicle of 6. Therefore if absolute certainty is required, a fascicle of triquetral leaves is best determined by actual count.

The transverse section of a leaf may be conveniently divided into three distinct parts—1, the dermal tissues, epiderm, hypoderm and stomata (fig. 17-a)—2, the green tissue, containing the resin-ducts (fig. 17-b)—3, the stelar tissues, enclosed by the endoderm and containing the fibro-vascular bundle (fig. 17-c).

THE DERMAL TISSUES OF THE LEAF.

The stomata of Pine leaves are depressed below the surface and interrupt the continuity of epiderm and hypoderm. They are wanting on the dorsal surface of the leaves of several Soft Pines, constantly in some species, irregularly in others. In Hard Pines, however, all surfaces of the leaf are stomatiferous. In several species of the Soft Pines the longitudinal lines of stomata are very conspicuous from the white bloom which modifies materially the general color of the foliage.

Under the action of hydrochloric acid the hypoderm is sharply differentiated from the epiderm by a distinct reddish tint, but without the aid of a reagent the two tissues do not always differ in appearance. The cells of epiderm and hypoderm may be so similar that they appear to form a single tissue. In most species, however, the epiderm is distinct, while the cells of the hypoderm are either uniform, with equally thin or thick walls—or biform, with very thin walls in the outer row of cells and very thick walls in the inner row or rows of cells—or multiform, with cell-walls gradually thicker toward the centre of the leaf. These conditions may be tabulated as follows—

Cells of epiderm and hypoderm similar fig. 19. Cells of epiderm and hypoderm distinct. Cells of hypoderm uniform, thin or thick figs. 20, 21. Cells of hypoderm biform fig. 22. Cells of hypoderm multiform fig. 23.

The biform hypoderm is not always obvious (clausa, Banksiana, etc.) where in some leaves there is but one row of cells. But with the examination of other leaves one or more cells of a second row will be found with very thick walls. Among Hard Pines there is no Old World species with a biform hypoderm. But there are a few American species with uniform hypoderm (resinosa, tropicalis, patula and Greggii); while, in some leaves of the few American Hard Pines with multiform hypoderm, the uniform hypoderm is a variation.

THE GREEN TISSUE.

In this tissue are the resin-ducts, each with a border of cells, corresponding in appearance and in chemical reaction with the cells of the hypoderm and with thinner or thicker walls. With reference to the green tissue the foliar duct may be in one of four positions.

1. External against the hypoderm fig. 24. 2. Internal against the endoderm fig. 28. 3. Medial in the green tissue, touching neither hypoderm nor endoderm fig. 26. 4. Septal touching both endoderm and hypoderm, forming a septum fig. 30.

Among the Soft Pines the external duct is invariable in the subsection Paracembra. It is also characteristic of the Strobi, where it is sometimes associated with a medial duct. In the Cembrae and the Flexiles, however, the ducts are external in some species, or medial or both in others, without regard to the affinities of these species.

Among the Hard Pines the external duct is characteristic of the Old World, there being but two American Pines with this character (resinosa and tropicalis). The internal duct is peculiar to Hard Pines of the New World, its presence in Old World species being extremely rare. The medial duct is common to species of both hemispheres, either alone or in association with ducts in other positions (figs. 25, 27). The septal duct is peculiar to a few species (oocarpa, tropicalis, and less frequently Pringlei and Merkusii). I have also seen it in a leaf of P. canariensis. The internal and septal ducts appear to be confined to the species of warm-temperate or tropical countries.

The number of resin-ducts of a single leaf may be limited to two or three (strobus, koraiensis, etc.), but in many species it is exceedingly variable and often large (pinaster, sylvestris, etc.). Eighteen or more ducts in a single leaf have been recorded. Such large numbers are peculiar to Pinus. Occasionally a single leaf, possibly the leaves of a single tree, may be without ducts, but this is never true of all the leaves of a species.

THE STELAR TISSUES.

The walls of the endoderm are, in most species, uniform, but, with P. albicaulis and some species of western North America, the outer walls of the cells are conspicuously thickened (fig. 32). Both thin and thick walls may be found among the leaves of the group Macrocarpae and of the species longifolia.

The fibro-vascular bundle of the leaf is single in Soft Pines, double in Hard Pines. This distinction is employed by Koehne as the basis of his two sections, Haploxylon and Diploxylon. The double bundle is usually obvious even when the two parts are contiguous, but they are sometimes completely merged into an apparently single bundle. This condition, however, is never constant in a Hard Pine, and a little investigation will discover a leaf with a true double bundle.

Some cells about the fibro-vascular bundle acquire thick walls with the appearance and chemical reaction of the hypoderm cells. Among the Soft Pines this condition is most obvious in the group Cembroides. Among the Hard Pines it appears in all degrees of development, being absent (figs. 24, 25), sometimes in irregular lines above and below the bundle (figs. 26, 27, 30, 31), or forming a conspicuous tissue between and partly enclosing the two parts of the bundle (figs. 28, 29).

The leaf-section furnishes sectional and other lesser distinctions. It is often decisive in separating species otherwise difficult to distinguish (nigra and resinosa or Thunbergii and sinensis, etc.). Sometimes it is sufficiently distinct to determine a species without recourse to other characters (tropicalis, oocarpa, Merkusii, etc.). An intimate knowledge of the leaf-section, with an understanding of the limits of its variation, is a valuable equipment for recognizing species.



THE FLOWERS. Plate III, figs. 33-39.

The flowers in Pinus are monoecious, the pistillate in the position of a long shoot, taking the place of a subterminal or lateral bud, the staminate in the position of a dwarf-shoot, taking the place of a leaf-fascicle but confined to the basal part of the internode.

Pistillate flowers are single or verticillate. On multinodal shoots they are often multiserial, appearing on two or more nodes of the same spring-shoot (fig. 33). On uninodal shoots they are necessarily subterminal (fig. 34), the lateral pistillate flower being possible only on multinodal shoots (fig. 35) where it is often associated with the subterminal flower (fig. 33). Like the multinodal shoot, on which its existence depends, the lateral pistillate flower cannot be employed for grouping the species. It is merely the frequent, but not the essential, evidence of condition of growth that is more perfectly characterized by the shoot itself.

Staminate catkins are in crowded clusters, capitate or elongate (figs. 36, 37), but with much variation in the number of catkins in each cluster. In P. rigida I have found single catkins or clusters of all numbers from two to seventy or more. In P. Massoniana and P. densiflora a cluster attains such unusual length (fig. 37) that this character becomes a valuable distinction between these species and P. sinensis, which has short-capitate clusters. The catkins differ much in size, the largest being found among the Hard Pines.

In the connective of the binate pollen-sacs there is a notable difference (figs. 38, 39), the smaller form being characteristic of the Soft Pines. But this is not invariable (excelsa, sylvestris, etc.), and the absence of complete data does not permit an accurate estimate of its importance.

THE CONELET. Plate III, figs. 40-45.

After pollination the pistillate flower closes and becomes the conelet, the staminate flowers withering and falling away. The conelet makes no appreciable growth until the following year. Like the pistillate flower it may be subterminal or lateral, but a subterminal pistillate flower may become a pseudolateral conelet by reason of a summer-growth (fig. 40-a). Such a condition may be recognized on the branchlets of the present, and of the previous year (fig. 40-b), by the very short internode and short leaves beyond the fruit.

The conelet offers some distinctions of form, of color, and of length of peduncle, while in some species (sylvestris, caribaea, etc.) its reflexed position is an important specific character. The most important distinctions, however, are found in its scales, which may be

1. entire subsection Cembra fig. 41. 2. tuberculate tropicalis, etc. fig. 42. 3. short-mucronate sylvestris, glabra, etc. fig. 43. 4. long-mucronate aristata, contorta, etc. fig. 44. 5. spinescent taeda, pungens, etc. fig. 45.



THE CONE. Plate IV.

The cone of Pinus shows great differences of color, form and tissue; these are useful for specific and sectional distinctions, while the gradual change from the primitive conditions of the Cembrae to the elaborate form, structure and mode of dissemination of some serotinous species are obvious evidence of an evolution among the species of remarkable taxonomic range. A form new among Coniferae appears, the oblique cone, and a new condition, the serotinous cone, both appearing at first alone and, finally, in constant association.

COLOR OF THE CONE.

With few exceptions the color of the ripe cone may be classified under one of the following shades of brown or yellow.

Nut-brown The stain of the walnut-husk. Rufous brown A pronounced reddish nut-brown. Fulvous brown A yellowish nut-brown. Tawny yellow The color of the lion. Orange Ochre-yellow to red-orange.

These colors may be paler or deeper. They may be obscured by a fuscous shade or may be modified by a dull or lustrous surface. The presence of two or more of these shades in a single species and the inherent difficulties of color description lessen the value of the character. Nevertheless certain allied species, such as P. nigra and Thunbergii, or P. densiflora and Massoniana, may be distinguished by the prevalent difference in the color of their cones.

DIMENSIONS OF THE CONE.

The cone is small, medium or large in different species, but varies greatly under the influences of environment or of individual peculiarities. The character possesses relative value only, for great variation is possible in the same locality and even on the same tree.

THE PEDUNCLE.

All conelets are pedunculate, but in some species the peduncle, even when long (patula), may become overgrown and concealed by the basal scales of the ripe cone. Articulation usually takes place between the peduncle and the branch, sometimes with the loss of a few basal scales which remain temporarily on the tree (ponderosa, palustris, etc.). With P. Nelsonii, and to a less degree with P. Armandi, there is articulation between the cone and its peduncle.

There are several species bearing persistent cones with no articulation. This condition appears in other genera, such as Larix and Picea, but without obvious significance. In Pinus, however, the gradual appearance of the persistent cone, for it is rare, common, prevalent or invariable in different species, and its essential association with the serotinous cone, suggest an evolution toward a definite end.

THE UMBO.

The exposed part of the scale of the conelet is the umbo of the ripe cone, a small definite area representing the earlier part of the biennial growth of the cone. The position of the umbo on the apophysis is the basis of Koehne's subdivision of the section Haploxylon.

1. Umbo terminal Subsection Cembra fig. 46-a. 2. Umbo dorsal Subsection Paracembra fig. 46-b.

Two other characters assist in establishing these subsections—the conelet, unarmed in Cembra, armed in Paracembra—the pits of the ray-cells of the wood, large in Cembra, small in Paracembra.

THE APOPHYSIS.

The apophysis represents the later and larger growth of the cone-scale. With a terminal umbo the margin of the apophysis is free and may be rounded (fig. 49) or may taper to a blunt point (fig. 52), and any extension of the scale is a terminal extension. With the dorsal umbo all sides of the apophysis are confined between other apophyses, and any extension is a dorsal thickening of the apophysis or a dorsal protuberance. The outline of an apophysis with a dorsal umbo is quadrangular, or it is irregularly pentagonal or hexagonal, the different forms depending on the arrangement of the contiguous scales, whether of definite or indefinite phyllotactic order, a distinction to be considered later.

The two positions of the umbo result from the relative growth of the dorsal and ventral surfaces of the cone-scale. With the terminal umbo the growth of both surfaces is uniform, with the dorsal umbo the growth is unequal. A true terminal umbo rests on the surface of the underlying scale, although several species with terminal umbos show the first stages of the dorsal umbo. The umbo of P. Lambertiana or of P. flexilis does not touch the surface of the scale below, and a small portion of the under side of the apophysis is brought into view on the closed cone. The cone of P. albicaulis (Plate VIII, fig. 90) shows all degrees of development between a terminal umbo near the apex of the cone and a dorsal umbo near its base.

The growth of the apophysis may be limited and constant (strobus, echinata, etc.) or exceedingly variable, ranging from a slight thickness to a long protuberance (pseudostrobus, montana, etc.). The protuberance is usually reflexed from the unequal growth of the two surfaces. With the terminal umbo the protuberance lengthens the scale, with the dorsal umbo it thickens the scale. It is sometimes a specific character (ayacahuite, longifolia) appearing on all cones of the species, sometimes a varietal form, associated in the same species with an unprolonged apophysis (sylvestris, montana).

On different parts of the same cone, base, centre or apex, the dimensions of the apophyses differ, but at each level the scales may be uniform on all sides of the cone. That is to say, the cone is symmetrical with reference to any plane passing through its axis. This, the symmetrical cone, is characteristic of all other genera of the Abietineae, and is invariable among the Soft Pines and in many Hard Pines (figs. 47, 48, 52, 54). But among the Hard Pines there is gradually developed a new form of cone with smaller flatter apophyses on the anterior, and larger thicker apophyses on the posterior surface. This is the peculiar oblique cone of Pinus (figs. 50, 51, 53), symmetrical with reference to one plane only, which includes the axis of both cone and branch. The oblique cone is a gradual development among the Hard Pines; in some species it is associated as a varietal form with the symmetrical cone, and finally, in some serotinous species, it is the constant form.

THE OBLIQUE CONE.

When the oblique cone is merely a varietal form (halepensis, etc.), it gives the impression of an accident, resulting from the reflexed position of the cone and the consequent greater development of the scales receiving a greater amount of light and air. But with the serotinous cones (radiata, attenuata), the advantages of this form become apparent. The cones of these species are in crowded nodal clusters, reflexed against the branch (fig. 50). The inner, anterior scales are perfectly protected by their position, while the outer, posterior scales are exposed to the weather. These last only are very thick; that is to say, there is an economical distribution of protective tissue, with the greatest amount where it is most needed. The oblique form is peculiarly adapted for a cone destined to remain on the tree for twenty years or more and to preserve its seeds unimpaired. Like the persistent cone, the oblique cone finds in association with the serotinous cone a definite reason for existence.



PHYLLOTAXIS. Plate V.

There is an obvious difference between the cones of the two sections of the genus. Those of the Soft Pines (figs. 55, 56) have larger and fewer scales, those of the Hard Pines (figs. 57, 58) have more numerous and smaller scales, in proportion to the size of the cone. The former condition represents a lower, the latter condition represents a higher, order of phyllotaxis.

DEFINITE PHYLLOTAXIS.

On a cylindrical axis with scales of the same size, the spiral arrangement would appear as in fig. 62, where the scales are quadrangular and any four adjacent scales are in mutual contact at their sides or angles. These four scales lie on four obvious secondary spirals (fig. 59, a-a, b-b, c-c, d-d). According to the phyllotactic order of the scales these may be the spirals of 2, 3, 5, 8 or of 3, 5, 8, 13 or of 5, 8, 13, 21 etc., etc., from which combinations the primary spiral, on which the scales are inserted on the cone-axis, can be easily deduced. Four quadrangular scales in mutual contact represent the condition of definite phyllotaxis. If the cone is conical, definite phyllotaxis would be possible among all the scales only when the size of the scales diminishes in equal measure with the gradual diminution of the cone's diameter. Such a hypothetical cone is shown in fig. 61.

INDEFINITE PHYLLOTAXIS.

On an imaginary cone of conical form and with scales of equal size throughout, there must be more scales about the base than about the apex of the cone. The phyllotactic conditions must differ, and the obvious spirals, in passing from base to apex, must undergo readjustment. If the scales at the base are in definite phyllotactic order and those at the apex are in the next lower order, it is evident that intermediate scales, in the gradual change from one condition to the other, must represent different conditions of indefinite phyllotaxis, while those in a central position on the cone may belong equally to either of two orders.

A Pine cone is never absolutely cylindrical nor do its scales vary in size proportionately to the change of diameter. Most of the scales of a cone are in indefinite phyllotactic relation, while definite phyllotaxis is found only at points on the cone.

As an extreme illustration, the cone of P. pinaster (fig. 60) shows four mutually contiguous quadrangular apophyses at (a), lying on the obvious spirals 5, 8, 13, 21, at (b) four similar apophyses on the spirals 3, 5, 8, 13, and at (c) four others on the spirals 2, 3, 5, 8. Between these three points are apophyses of irregular pentagonal or hexagonal outline, with three scales only in mutual contact (figs. 63, 64). Such are the majority of the scales of the cone and represent more or less indefinite conditions of phyllotaxis.

The cones of Hard Pines, by reason of relatively more and smaller scales and of a more conical form, attain a higher phyllotaxis and a more complex condition, two or even three orders being represented on a single cone; while the cones of Soft Pines, by reason of relatively fewer and larger scales and a more cylindrical form, are of lower phyllotaxis, with one order only more or less definitely presented. Therefore phyllotaxis furnishes another distinction between the two sections of the genus, but its further employment is exceedingly restricted on account of the constant repetition of the same orders among the species.



THE CONE-TISSUES. Plate VI.

The axis of the cone is a woody shell, enclosing a wide pith and covered by a thick cortex traversed by resin-ducts. By removing the scales and cortex from the axis (fig. 65) the wood is seen to be in sinuous strands uniting above and below fusiform openings, the points of insertion of the cone-scales. From the wood, at each insertion, three stout strands enter the scale, dividing and subdividing into smaller tapering strands whose delicate tips converge toward the umbo. Fig. 70 represents a magnified cross-section of half the cone-scale of P. Greggii; at (a) is a compact dorsal plate of bast cells; at (e) is a ventral plate of the same tissue but of less amount; at (b) is the softer brown tissue enclosing the wood-strands (d, d) (the last much more magnified in fig. 69) and the resin-ducts (e, e).

WOOD STRANDS.

The wood-strands, forming the axis of the cone, differ in tenacity in the two sections of the genus. Those of the Soft Pines are easily pulled apart by the fingers, those of the Hard Pines are tougher in various degrees and cannot be torn apart without the aid of a tool. This difference is correlated with differences in other tissues, all of them combining in a gradual change from a cone of soft yielding texture to one of great hardness and durability.

If a cone scale of P. ayacahuite is stripped of its brown and bast tissues (fig. 66) and is immersed in water and subsequently dried, there is at first a flexion toward the cone-axis (fig. 67) and then away from it (fig. 68). The wood-strands are hygroscopic and cooperate with the bast tissues in opening and closing the cone. This appears to be true of all species excepting the three species of the Cembrae, whose strands are so small and weak that they are not obviously affected by hygrometric changes.

BAST TISSUE.

With the exception of the three species of the Cembrae the inner part of the cone-scales is protected by sclerenchymatous cells forming hard dorsal and ventral plates (fig. 70, a, c). In Soft Pines these cells are subordinate to the more numerous parenchymatous cells, but in Hard Pines the sclerenchyma increases in amount until, among the serotinous species, it is the predominating tissue of the cone-scale, giving to these cones their remarkable strength and durability.

This bast tissue is hygroscopic and, with its greater thickness on the dorsal surface, there is a much greater strain on that side of the scale, tending to force the scales apart when they are ripe and dry, and subsequently closing and opening the cone on rainy and sunny days.

The cone, during the second season's growth, is completely closed, its scales adhering together with more or less tenacity. In most species the hygroscopic energy of the scales is sufficient to open the cone under the dry condition of its maturity, but with several species the adhesion is so persistent that some of the cones remain closed for many years. These are the peculiar serotinous cones of the genus.

THE SEROTINOUS CONE.

As an illustration of the area to which the adhesion is confined, a section may be sawed from a cone of P. attenuata (fig. 71). The axis and the scales that have been severed from their apophyses (b) can be easily pushed out of the annulus (a), which is composed wholly of apophyses so firmly adherent that they will successfully resist a strong effort to break them apart. When immersed in boiling water, however, the ring falls to pieces. An examination of these pieces discovers adhesion only on a narrow ventral border under the apophysis and on a corresponding dorsal border back of the apophysis. The rest of the scale is not adherent, so that the seed is free to fall at the opening of the cone.

The serotinous cone is a gradual development, wanting in most species, rare in a few, less or more frequent in others. A similar evolution of the persistent cone, of the oblique cone and of the cone-tissues has been already discussed. All these progressive characters culminate in mutual association in P. radiata and its allies. The result is a highly specialized fruit that should convey taxonomic significance of some kind.

With all serotinous species that I have seen, some of the trees open their cones at maturity, others at indefinite intervals. That is to say, the seed of a prolific year is not at the mercy of a single, perhaps unfavorable season. The chances of successful germination are much increased by the intermittent seed-release peculiar to these Pines. Such a method of dissemination must accrue to the advantage of a species. In other words, this intermittent dissemination and the oblique form of cone with its perfected tissues all mark the highest development of the genus.

THE SEED. Plate VI. Figs. 72-79.

The seed of Pinus contains an embryo, with the cotyledons clearly defined, embedded in albumen, which is protected by a bony testa with an external membranous spermoderm, produced, in most species, into an effective wing. While the seed of other genera of the Abietineae shows no striking difference among the species, that of Pinus is remarkably variable, presenting alike the most primitive and the most elaborate forms among the Conifers. These differences are valuable for the segregation of kindred species and for some specific distinctions.

WINGLESS SEEDS.

With wingless seeds the main distinction is found in the spermoderm, which is entire in one species only, P. koraiensis. In P. cembra it is wanting on the ventral surface of the nut, but on the dorsal surface, it is adnate partly to the nut, partly to the cone-scale. The nut of P. albicaulis and that of P. cembroides are quite bare of membranous cover. The spermoderm of P. flexilis is reduced to a marginal border, slightly produced into a rudimentary wing adnate to the nut.

THE ADNATE WING.

In P. strobus, longifolia and their allies and in P. Balfouriana the spermoderm is prolonged into an effective wing-blade from a marginal adnate base like that of P. flexilis. This adnate wing cannot be detached without injury.

THE ARTICULATE WING.

The articulate wing can be removed from the nut and can be replaced without injury. An ineffective form of this wing is seen in the Gerardianae and in P. pinea, where the blade is very short and the base has no effective grasp on the nut.

The base of the effective articulate wing contains hygroscopic tissue which acts with the hygroscopic tissue of the cone-scales. The dry conditions that open the cone and release the seeds cause the bifurcate base of the wing to grasp the nut more firmly.

This articulate wing is found in P. aristata and in all Hard Pines except P. pinea, longifolia and canariensis. The wing-blade is usually membranous throughout, but in some species there is a thickening of the base of the blade that meets the membranous apical part in an oblique line along which the wing is easily broken apart. This last condition attains in P. Coulteri and its associates a remarkable development.

Plate VI, fig. 72 shows the wingless seed of P. cembroides; fig. 73 represents the seed of P. flexilis, with a rudimentary wing; fig. 74 shows two seeds of P. strobus, intact and with the wing broken away; fig. 75 represents the articulate wing, whose bifurcate base when wet (fig. 76) tends to open and release the nut. When dry (fig. 77) the forks of the base, in the absence of the nut, close together and cross their tips; figs. 78, 79 show the peculiar reinforced articulate wing of P. Coulteri.

Such wide variation in so important an organ suggests generic difference. But here we are met by the association of the different forms in species evidently closely allied. The two Foxtail Pines are so similar in most characters that they have been considered, with good reason, to be specifically identical; yet the seed-wing of P. Balfouriana is adnate, that of P. aristata articulate. P. Ayacahuite produces not only the characteristic wing of the Strobi, adnate, long and effective, but also, in the northern variety, a seed with a rudimentary wing, the exact counterpart of the seed of P. flexilis. In both sections of the genus are found the effective adnate wing (Strobi and Longifoliae) and the inefficient articulate wing (Gerardianae and Pineae). A little examination of all forms of the seed will show that they blend gradually one into another.

The color of the wing is occasionally peculiar, as in the group Longifoliae. There is usually no constancy in this character, for the wing may be uniform in color or variously striated in seeds of the same species. The length and breadth of the seed-wing, being dependent on the varying sizes of the cone-scale, differ in the same cone. They are also inconstant in different cones of the same species, and of this inconstancy the seed of P. ayacahuite furnishes the most notable example.



THE WOOD. Plate VII.

With the exception of the medullary rays, a very small proportion of the whole, the wood of Pinus, as seen in cross-section (fig. 82), is a homogeneous tissue of wood-tracheids with interspersed resin-ducts. In tangential section the medullary rays appear in two forms, linear, without a resin-duct, and fusiform, with a central resin-duct. In radial section the cells of the linear rays are of two kinds, ray-tracheids, forming the upper and lower limits of the ray, characterized by small bordered pits, and ray-cells, between the tracheids, characterized by simple pits.

The walls of the ray-tracheids may be smooth or dentate; the pits of the ray-cells may be large or small. These conditions admit of four combinations, all of which appear in the medullary rays of Pinus, and of which a schematic representation is given in Plate VII. These combinations are

Ray-tracheids with smooth walls. Soft Pines. Ray-cells with large pits Subsection Cembra fig. 80. Ray-cells with small pits Subsection Paracembra fig. 81.

Ray-tracheids with dentate walls. Hard Pines. Ray-cells with large pits Group Lariciones fig. 83. Ray-cells with small pits Other Hard Pines fig. 84.

This, the simplest classification of Pine-wood, is not without exceptions. P. pinea of the Hard Pines resembles, in its wood-characters, P. Gerardiana and P. Bungeana of the Soft Pines. The dentate ray-tracheids of P. longifolia are not always obvious. The tracheids of P. luchuensis, according to Bergerstein (Wiesner Festschr. 112), have smooth walls. My specimen shows dentate tracheids. There is also evidence of transition from small to large pits (I. W. Bailey in Am. Nat. xliv. 292). Both large and small pits appear in my specimen of P. Merkusii.

Of other wood-characters, the presence or absence of tangential pits in the tracheids of the late wood establishes a distinction between Soft and Hard Pines. These pits, however, while always present in Soft Pines, are not always absent in Hard Pines. The single and multiple rows of resin-ducts in the wood of the first year may prove to be a reliable sectional distinction, but this character has not been sufficiently investigated to test its constancy. The wood-characters, therefore, however decisive they may be for establishing the phylogenetic relations of different genera, must be employed in the classification of the Pines with the same reservations that apply to external characters.

Ray-tracheids with dentate walls and ray-cells with large pits are peculiar to Pinus. Therefore the presence of these characters, alone or in combination, is sufficient evidence for the recognition of Pine-wood. But the combination of smooth tracheids with small pits (subsection Paracembra) Pinus shares with Picea, Larix and Pseudotsuga.

Among Hard Pines the size of the pits has a certain geographical significance. The large pits are found in all species of the Old World except P. halepensis and P. pinaster; the small pits in all species of the New World except P. resinosa and P. tropicalis. The Asiatic P. Merkusii with both large and small pits is not strictly an exception to this geographical distinction. The four exceptional species by this and by other characters unite the Hard Pines of the two hemispheres.

THE BARK.

Bark is the outer part of the cortex that has perished, having been cut off from nourishment by the thin hard plates of the bark-scales. In the late and early bark-formation is found a general but by no means an exact distinction between Soft and Hard Pines. In the Soft Pines the cortex remains alive for many years, adjusting itself by growth to the increasing thickness of the wood. The trunks of young trees remain smooth and without rifts. In the Hard Pines the bark-formation begins early and the trunks of young trees are covered with a scaly or rifted bark. The smooth upper trunk of older trees is invariable in Soft Pines, but in Hard Pines there are several exceptions to early bark-formation. These exceptions are easily recognized in the field, and the character is of decisive specific importance (glabra, halepensis, etc.).

Among species with early bark-formation are two forms of bark: 1, cumulative, sufficiently persistent to acquire thickness and the familiar dark gray and fuscous-brown shades of bark long exposed to the weather; 2, deciduous, constantly falling away in thin scales and exposing fresh red inner surfaces. The latter are commonly known as Red Pines, as distinguished from Black Pines with dark cumulative bark. Deciduous bark changes after some years to cumulative bark, and the upper trunk only of mature trees is red. Red Pines, although usually recognizable by their bark, are by no means constant in this character. Oecological or pathological influences may check the fall of the bark-scales, and then the distinction between the upper and lower parts of the trunk becomes lost.



SUMMARY

The various characters that have been considered in the previous pages may be classified under different heads, some of them applicable to the whole genus, others to larger or smaller groups of species.

GENERIC CHARACTERS

Several characters, quite distinct from those of other genera, are common to all the species.

1. The primary leaf—appearing as a scale or bract throughout the life of the tree. 2. The bud—its constant position at the nodes. 3. The internode—its three distinct divisions. 4. The secondary leaves—in cylindrical fascicles with a basal sheath. 5. The pistillate flower—its constant nodal position and its verticillate clusters. 6. The staminate flower—its constant basal position on the internode and its compact clusters. 7. The cone—its clearly defined annual growths.

Pinus is also peculiar in the dimorphism of shoots and leaves and in their constant interrelations with the diclinous flowers. Evolutionary processes develop features peculiar to Pinus alone (the oblique cone, etc.), but confined to a limited number of species.

SECTIONAL CHARACTERS

There are several characters that actually or potentially divide the genus into two distinct sections, popularly known as Soft and Hard Pines.

1. The fibro-vascular bundle of the leaf, single or double. 2. The base of the bract subtending the leaf-fascicle, non-decurrent or decurrent 3. The phyllotaxis of the cone, simple or complex. 4. The flower-bud, its less or greater development.

Some characters indicate the same distinction but are subject each to a few exceptions.

5. The fascicle-sheath, deciduous or persistent. 6. The walls of the ray-tracheids, smooth or dentate. 7. The connective of the pollen-sacs, large or small. 8. The formation of bark, late or early.

SUBSECTIONAL CHARACTERS

An exact subdivision of the Soft Pines is possible on the following characters.

1. The umbo of the cone-scales, terminal or dorsal. 2. The scales of the conelet, mutic or armed. 3. The pits of the ray-cells, large or small.

EVOLUTIONAL CHARACTERS

The progressive evolution of the fruit of Pinus, from a symmetrical cone of weak tissues, bearing a wingless seed, to an indurated oblique cone with an elaborate form of winged seed and an intermittent dissemination, appears among the species in various degrees of development as follows—

The seed

1. wingless. 2. with a rudimentary wing. 3. with an effective adnate wing. 4. with an ineffective articulate wing. 5. with an effective articulate wing. 6. with an articulate wing, thickened at the base of the blade.

The cone

1. indehiscent. 2. dehiscent and deciduous. 3. dehiscent and persistent. 4. persistent and serotinous.

and as to its form

5. symmetrical. 6. subsymmetrical. 7. oblique.

These different forms of the seed and, to some extent, of the cone, are available for segregating the species into groups of closely related members; while the gradual progression of the fruit, from a primitive to a highly specialized form of cone and method of dissemination, points to a veritable taxonomic evolution which is here utilized as the fundamental motive of the systematic classification of the species.

SPECIFIC CHARACTERS

All aspects of vegetative and reproductive organs may contribute toward a determination of species, but the importance of each character is often relative, being conclusive with one group of species, useless with another. Characters considered by earlier authors to be invariable with species, such as the dimensions of leaf or cone, the number of leaves in the fascicle, the position of the resin-ducts, the presence of pruinose branchlets, etc., prove to be inconstant in some species. In fact, as the botanical horizon enlarges, the varietal limits of the species broaden and many restrictions imposed by earlier systems are gradually disappearing.

Variation is the preliminary step toward the creation of species, which come into being with the elimination of intermediate forms. Variation in a species may be the result of its participation in the evolutionary processes culminating in the serotinous Pines, or it may result from the ability of the species to adapt itself to various environments by sympathetic modifications of growth, or it may arise from some peculiarity of the individual tree.

Evolutionary variation is associated with the gradual appearance of the persistent, the oblique and the serotinous cone, and of the multinodal spring-shoot. For these conditions appear in less or greater prevalence among the species of the genus.

Variation induced by environment finds familiar illustrations among the species that can survive at the limits of vegetation and can meet these inhospitable conditions by a radical change of all growing parts. Such variations are mainly of dimensions, but, with some species, the number of fascicle-leaves is affected and the shorter growing-season may modify the cone-tissues. In Mexico and Central America are found extremes of climate within small areas and easily within the range of dissemination from a single tree. The cause of the bewildering host of varietal forms, connecting widely contrasted extremes, seems to lie in the facile adaptability of those Pines, which are able to spread from the tropical base of a mountain to a less or greater distance toward its snow-capped summit.

The peculiarities of individual trees that induce abnormally short or long growths, the dwarf or other monstrous forms, the variegations in leaf-coloring, etc., etc., are not available for classification, for they may appear in any species, in fact in any genus of Conifers. These variations are artificially multiplied for commercial and decorative purposes. But inasmuch as they are repeated in all species and genera of the Coniferae that have been long under the observation of skillful gardeners, their significance has a broader scope than that imposed by the study of a single genus.



PART II

CLASSIFICATION OF THE SPECIES

The following classification is based on the gradual evolution of the fruit from a cone symmetrical in form, parenchymatous in tissue, indehiscent and deciduous at maturity, releasing its wingless seed by disintegration—to a cone oblique in form, very strong and durable in tissue, persistent on the tree, intermittently dehiscent, releasing its winged seeds partly at maturity, partly at indefinite intervals during several years. This evolution embraces two extreme forms of fruit, one the most primitive, the other the most elaborate, among Conifers.

Two sections of the genus, Soft and Hard Pines, are distinguished by several correlated characters, and moreover are distinct by obvious differences in the tissues of their cones as well as in the quality and appearance of their wood.

With the Soft Pines the species group naturally under two subsections on the position of the umbo, the anatomy of the wood and the armature of the conelet. In one subsection (Cembra) are found three species, P. cembra and its allies, with the cone-tissues so completely parenchymatous that the cones cannot release the seeds except by disintegration. In both subsections there is a gradual evolution from a wingless nut to one with an effective wing, adnate in one subsection, adnate and articulate in the other. The different stages of this evolution are so distinct that the Soft Pines are easily separated into definite groups.

Among the Hard Pines a few species show characters that are peculiar to the Soft Pines. These exceptional species form a subsection (Parapinaster) by themselves.

With the remaining species, the majority of the Pines, the distinctions that obtain among Soft Pines have disappeared. The dorsal umbo, the articulate seed-wing, the persistent fascicle-sheath, the dorsal and ventral stomata of the leaf and its serrate margins, the dentate walls of the ray-tracheids have become fixed and constant. But a new form of seed-wing appears, with a thickened blade, assuming such proportions in P. Sabiniana and its two allies that these three constitute a distinct group, remarkable also for the size of its cones.

Here also appear a new form of fruit, the oblique cone, and a new method of dissemination, the serotinous cone. Associated with the latter are the persistent cone and the multinodal spring-shoot. These characters do not develop in such perfect sequence and regularity that they can be employed for grouping the species without forcing some of them into unnatural association. The oblique cone first appears sporadically here and there and without obvious reason. The persistent cone, the first stage of the serotinous cone, is equally sporadic in the earlier stages of evolution. The same may be said of the multinodal shoot.

Nevertheless these characters show an obvious progression toward a definite goal, where they are all united in a small group of species remarkable for the form and texture of their cones, for a peculiar seed-release and for the vigor and rapidity of their growth. It is possible, with the assistance of other characters, to segregate these species in three groups in which the affinities are respected and the general trend of their evolution is preserved.

The first group, the Lariciones, contains species with large ray-pits, cones dehiscent at maturity, and uninodal spring-shoots. They are, with two exceptions, P. resinosa and P. tropicalis, Old World species.

The second group, the Australes, contains species with small ray-pits, cones dehiscent at maturity and spring-shoots gradually changing, among the species, from a uninodal to a multinodal form. They are, without exception, species of the New World.

The third group, the Insignes, contains the serotinous species. The ray-pits are small and the spring-shoots are, with two exceptions, multinodal. With two exceptions, P. halepensis and P. pinaster, they are New World species.

These three groups, being the progressive sequence of a lineal evolution, are not absolutely circumscribed, but are more or less connected through a few intermediate species of each group. The systematic position of these intermediate species is determined by their obvious affinities. It cannot be expected that the variations, which take an important part in the evolution of the species, progress with equal step or in perfect correlation with each other.

As to specific determinations, a little experience in the field discloses an amount of variation in species that does not always appear in the descriptions of authors; and species that are under the closest scrutiny of botanists, foresters or horticulturalists, attest by their multiple synonymy their wide variation. The possibilities of variation are indefinite and, with adaptable Pines, the range of variation is somewhat proportionate to change of climate. In mountainous countries, where there are warm sheltered valleys with rich soil below cold barren ledges, the most variable Pines are found. The western species of North America, for instance, are much more variable than the eastern species, while in Mexico, a tropical country with snow-capped mountains, the variation is greatest.

Therefore in the limitation of species undue importance should not be given to characters responsive to environment, such as the dimensions of leaf or cone, the number of leaves in the fascicle, etc. Moreover, there are familiar examples (P. sylvestris, etc.) that show the possibility of wide differences in the cone of the same species.

In the following classification species only are considered without attempting to determine varietal or other subspecific forms. But varieties are often mentioned as one of the factors illustrating the scope of species. Synonymy serves a like purpose, but synonyms not conveying useful information are omitted, Roezl's list of Mexican species, for instance, and variations in the orthography of specific names.

PINUS

1755 Pinus Duhamel, Traite des Arbres, ii. 121. 1790 Apinus Necker, Elem. Bot. iii. 269. 1852 Cembra Opiz, Seznam, 27. 1854 Strobus Opiz, Lotos, iv. 94. 1903 Caryopitys Small, Fl. Southeast. U. S. 29.

Leaves and shoots dimorphous, primary leaves on long shoots, secondary leaves on dwarf shoots. Flowers diclinous, the pistillate taking the place of long shoots, the staminate taking the place of dwarf shoots. Growth of wood and fruit emanating from the nodes; buds, branchlets and cones, therefore, in verticillate association. Leaves and staminate flowers in internodal position, the primary leaves along the whole length of the internode, subtending secondary leaf-fascicles on the apical, staminate flowers on the basal part. Buds compounded of minute buds in the axils of bud-scales, becoming the bracts of the spring-shoot. Branchlets of one or more internodes, each internode in three parts—a length without leaves, a length bearing leaves and a node of buds. Cone requiring two, rarely three years to mature, displaying its annual growths by distinct areas on each scale. Seeds wingless or winged, edible and nutritious.

The Pines are confined to the northern hemisphere, but grow in all climates and under all conditions of soil, temperature and humidity where trees can grow. Some of the species are of very restricted range, but others are adaptable and can cover wide areas. The sixty-six species are distributed as follows—

Eastern Hemisphere, 23.

1 exclusively African (Canary Islands). 2 exclusively European. 3 about the Mediterranean Basin. 2 common to Europe and northern Asia. 14 exclusively Asiatic.

Western Hemisphere, 43.

28 in western North America, of which 12 are confined to Mexico and Central America. 15 in eastern North America, of which 2 are exclusively West Indian.

The two sections of the genus correspond with those of Koehne (Deutsch. Dendrol. 28 [1893]) and his two names, Haploxylon and Diploxylon, are adopted here, together with his two subsections of Haploxylon, Cembra and Paracembra.

Of the two subsections of Diploxylon, Pinaster has been employed by Endlicher (Syn. Conif. 166 [1847]) and later authors for smaller or larger groups of Hard Pines. The subsection Parapinaster is now proposed.

The names of groups, Cembrae, Strobi, Cembroides, Gerardianae, Balfourianae, Pineae, Lariciones and Australes, are taken from Engelmann's Revision of the Genus Pinus (Trans. Acad. Sci. St. Louis, iv. 175-178 [1880]). The remainder, Flexiles, Leiophyllae, Longifoliae, Insignes and Macrocarpae, are here proposed.

In order to bring the illustrations within the limits of the page the dimensions of cone and leaf, as shown on the plates, are a little smaller than life. In plates X and XXV the reproductions of the cones are reduced to 2/5 life-size.

SECTIONS, SUBSECTIONS, AND GROUPS

Bases of the fascicle-bracts non-decurrent A—HAPLOXYLON

Umbo of the cone-scale terminal a—Cembra

Seeds wingless. Cones indehiscent I. Cembrae Cones dehiscent II. Flexiles Seed with an adnate wing III. Strobi

Umbo of the cone-scale dorsal b—Paracembra

Seeds wingless IV. Cembroides Seed-wing short, ineffective V. Gerardianae Seed-wing long, effective VI. Balfourianae

Bases of the fascicle-bracts decurrent B—DIPLOXYLON

Fascicle-sheath or seed of Haploxylon c—Parapinaster

Fascicle-sheath deciduous VII. Leiophyllae Fascicle-sheath persistent. Seed-wing of the Strobi VIII. Longifoliae Seed-wing of the Gerardianae IX. Pineae

Fascicle-sheath persistent, seed-wing articulate, effective d—Pinaster

Base of wing-blade thin or slightly thickened. Cones dehiscent at maturity. Pits of ray-cells large X. Lariciones Pits of ray-cells small XI. Australes Cones serotinous, pits of ray-cells small XII. Insignes Base of wing-blade very thick XIII. Macrocarpae



HAPLOXYLON

Bases of the bracts subtending leaf-fascicles not decurrent. Staminate flowers not sufficiently developed in the bud to be apparent. Spring-shoots uninodal. Fibro-vascular bundle of the leaf single. Cone symmetrical, of relatively fewer larger scales, its tissues softer. Bark-formation late, the trunks of young trees smooth. Wood soft and with little resin, of uniform color and with relatively obscure definition of the annual rings. Tracheids of the medullary rays with smooth walls.

All the species of this section, except P. Nelsonii, have deciduous fascicle-sheaths. There are but two species of Diploxylon with deciduous sheaths, P. leiophylla and P. Lumholtzii, both of them easily recognized. The deciduous sheath, therefore, is an obvious and useful means for recognizing the Soft Pines. On the characters of the fruit and the wood Haploxylon can be divided into two subsections.

a. Cembra Umbo of the cone-scale terminal. b. Paracembra Umbo of the cone-scale dorsal.

Cembra

Umbo of the cone-scale terminal. Scales of the conelet unarmed. Leaves in fascicles of 5, the sheath deciduous, the two dermal tissues distinct, the hypoderm-cells uniform. Pits of the cells of the wood-rays large.

Seeds wingless. Cones indehiscent I. Cembrae. Cones dehiscent II. Flexiles. Seeds with an adnate wing III. Strobi.

I. CEMBRAE

Seeds wingless. Cones indehiscent, deciduous at maturity.

In this group of species there is no segregation of sclerenchyma into an effective tissue. The cones are inert under hygrometric changes and may always be recognized in herbaria by their persistent occlusion and soft tissues. The seeds are released only by the disintegration of the fallen cone. There is, however, a vicarious dissemination by predatory crows (genus Nucifraga) and rodents.

Leaves serrulate, their stomata ventral only. Cones relatively larger, the apophyses protuberant 1. koraiensis. Cones relatively smaller, the apophyses appressed 2. cembra. Leaves entire, their stomata ventral and dorsal 3. albicaulis.



1. PINUS KORAIENSIS

1784 P. strobus Thunberg, Fl. Jap. 275 (not Linnaeus). 1842 P. koraiensis Siebold & Zuccarini, Fl. Jap. ii. 38. 1857 P. mandschurica Ruprecht in Bull. Acad. Sci. St. Petersb. xv. 382.

Spring-shoots more or less densely tomentose. Leaves from 8 to 12 cm. long, serrulate, stomata ventral only, resin-ducts medial and confined to the angles. Conelets large, subterminal, or on young trees often pseudolateral. Cones indehiscent, from 9 to 14 cm. long, short-pedunculate, ovoid-conical or subcylindrical; apophyses dull pale nut-brown, rugose, shrinking much in drying and exposing the seeds, prolonged and tapering to a more or less reflexed tip, the umbo inconspicuous; seeds large, wingless, the spermoderm entire.

A species of the mountains of northeastern Asia with valuable wood and large edible nuts; hardy and often cultivated in cool-temperate climates.

The P. koraiensis of Beissner (in Nuov. Giorn. Bot. Ital. n. ser. iv. 184) and of Masters (in Gard. Chron. ser. 3, xxxiii. 34, ff.) are P. Armandi and have led to an erroneous extension of the range of this species into Shensi and Hupeh. In the original description of the species the authors call attention to an error in the plate, where a cone of another species has been substituted.

P. koraiensis resembles P. cembra in leaf and branchlet but not in the cone. It is often confused with P. Armandi, but can easily be distinguished by its tomentose branchlets, indehiscent cone and peculiar seed. The two species, moreover, do not always agree in the position of the foliar resin-ducts.

Plate VIII.

Fig. 85, Cone and seed. Fig. 86, Leaf-fascicle and magnified leaf-section.

2. PINUS CEMBRA

1753 P. cembra Linnaeus, Sp. Pl. 1000. 1778 P. montana Lamarck, Fl. Franc. iii. 651 (not Miller). 1858 P. pumila Regel in Index Sem. Hort. Petrop. 23. 1884 P. mandschurica Lawson, Pinet. Brit. i. 61, ff. (not Ruprecht). 1906 P. sibirica Mayr, Fremdl. Wald- & Parkb. 388. 1913 P. coronans Litvinof in Trav. Mus. Bot. Acad. St. Petersb. xi. 23, f.

Spring-shoots densely tomentose. Leaves from 5 to 12 cm. long, serrulate; stomata ventral only; resin-ducts medial or, in the dwarf form, often external. Conelets short-pedunculate, purple during their second season. Cone from 5 to 8 cm. long, ovate or subglobose, subsessile; apophyses dull nut-brown, thick, slightly convex, the margin often a little reflexed, the umbo inconspicuous; seeds wingless, large, the dorsal spermoderm adnate partly to the nut, partly to the cone-scale, the ventral spermoderm wanting.

The Swiss Stone Pine attains a height of 15 or 25 metres and occupies two distinct areas, the Alps, from Savoy to the Carpathians at high altitudes, and the plains and mountain-slopes throughout the vast area from northeastern Russia through Siberia. Beyond the Lena and Lake Baikal it becomes a dwarf (var. pumila) with its eastern limit in northern Nippon and in Kamchatka. It is successfully cultivated in the cool-temperate climates of Europe and America. The wood is of even, close grain, peculiarly adapted to carving. The nuts are gathered for food and confections, but are destroyed in great numbers by squirrels, mice and a jay-like crow, the European Nutcracker. It is generally conceded, however, that these enemies assist in dissemination.

Plate VIII.

Fig. 87, Cone, seed and magnified leaf-section. Fig. 88, Tree at Arolla, Switzerland. Fig. 89, Cone, leaf-fascicle and magnified leaf-section of var. pumila.

3. PINUS ALBICAULIS

1853 P. flexilis Balfour in Bot. Exped. Oregon, 1, f. (not James). 1857 P. cembroides Newberry in Pacif. R. R. Rep. vi-3, 44, f. (not Zuccarini). 1863 P. albicaulis Engelmann in Trans. Acad. Sci. St. Louis, ii. 209. 1867 P. shasta Carriere, Trait. Conif. ed. 2, 390.

Spring-shoots glabrous or pubescent. Branchlets pliant and tough. Leaves from 4 to 7 cm. long, entire, stout, persistent for several years; stomata dorsal and ventral; resin-ducts external. Conelets short-pedunculate, dark purple during the second season, their scales often tapering to an acute apex. Cones from 5 to 7 cm. long, subsessile, oval or subglobose; apophyses nut-brown or fulvous brown, dull or slightly lustrous, very thick, the under surface conspicuous, meeting the upper surface in an acute margin, and terminated by a salient, often acute umbo; seed wingless, the testa bare of spermoderm.

This species ranges from British Columbia through Washington and Oregon, over the mountains of northern California and the Sierras as far south as Mt. Whitney, and, on the Rocky Mountains, through Idaho and Montana to northern Wyoming. It is found at the timber-line of many stations and forms, in exposed situations, flat table-like masses close to the ground. It is a species of no economical importance and is too inaccessible for the profitable gathering of its large nuts, which are devoured in quantity by squirrels and by Clark's crow, a bird of the same genus with the pinivorous Nutcracker of Europe.

P. albicaulis is distinguished from its allies by its entire leaves with both dorsal and ventral stomata, from P. flexilis by its indehiscent cone, and from all of these species by its seed without membranous cover or rudimentary wing. It was united with P. flexilis by Parlatore and Gordon, and, later, was referred to that species as a varietal form by Engelmann (in Brewer & Watson, Bot. Calif. ii. 124). Parrish's P. albicaulis (in Zoe, iv. 350), extending its range to the mountains of southern California, proves to be P. flexilis (Jepson, Silva Calif. 74).

Plate VIII.

Fig. 90, Two cones and seed. Fig. 91, Leaf-fascicle. Fig. 92, Magnified leaf-section.



II. FLEXILES

Seeds wingless, the spermoderm forming a narrow border with a rudimentary prolongation. Cones dehiscent at maturity.

The dehiscent cone distinguishes this group from the Cembrae. Therefore confusion of P. koraiensis with P. Armandi, or P. albicaulis with P. flexilis should be impossible. The peculiar seed is found again only in the northern variety of P. ayacahuite.

Leaves usually entire, the stomata dorsal and ventral 4. flexilis. Leaves serrulate, the stomata ventral only 5. Armandi.

4. PINUS FLEXILIS

1823 P. flexilis James in Long's Exped. ii. 34. 1882 P. reflexa Engelmann in Bot. Gaz. vii. 4. 1897 P. strobiformis Sargent, Silva N. Am. xi. 33, tt. 544, 545 (not Engelmann).

Spring-shoots pubescent; branchlets very tough and pliant. Leaves from 3 to 9 cm. long, entire, or serrulate in the southern variety, persistent for five or six years; stomata dorsal and ventral or, in the south, sometimes ventral only; resin-ducts external. Cones from 6 to 25 cm. long, ovate or subcylindrical, short-pedunculate; apophyses pale tawny yellow, or yellow ochre, lustrous, often prolonged and more or less reflexed, thick, the margin together with the umbo raised above the surface of the cone.

This species grows on the Rocky Mountains from Alberta in the Dominion of Canada to Chihuahua in northern Mexico and ranges westward to the eastern slope of the Sierras and to the southern mountains of California. The wood, where accessible, is manufactured into lumber. It may be seen in the Arnold Arboretum and in the Royal Gardens at Kew.

P. flexilis is recognized by its lustrous yellow cones. This and the constantly external ducts of its usually entire leaves distinguish it from P. Armandi. From P. albicaulis, with similar leaves, it differs by its dehiscent cone. At one extreme the cone of P. flexilis is not unlike that of P. albicaulis, at the other extreme it approaches the characteristic cone of P. ayacahuite, with prolonged reflexed scales. Hence the confusion of P. albicaulis with P. flexilis (Murray, Parlatore and others) and of P. flexilis with Engelmann's P. strobiformis. Sargent's P. strobiformis, illustrated in the Silva of North America, is the form of this species known as var. reflexa of Engelmann.

Plate IX.

Fig. 93, Two cones and seed. Fig. 94, Leaf-fascicle. Fig. 95, Magnified leaf-section.

5. PINUS ARMANDI

1884 P. Armandi Franchet in Nouv. Arch. Mus. Paris, ser. 2, vii. 95, 96, t. 12. 1898 P. scipioniformis Masters in Bull. Herb. Boiss. vi. 270. 1903 P. koraiensis Masters in Gard. Chron. ser. 3, xxxiii. 34, ff. 18, 19 (not Siebold & Zuccarini). 1908 P. Mastersiana Hayata in Gard. Chron. ser. 3, xliii, 194.

Spring-shoots glabrous; branches and most of the trunk covered with a smooth gray cortex. Leaves from 8 to 15 cm. long, serrulate; stomata ventral only; resin-ducts external, external and medial, or medial, all three conditions sometimes occurring in leaves of the same branchlet. Cones from 6 to 20 cm. in length, pendent on peduncles of various lengths, the peduncle often remaining on the tree after the fall of the cone; apophyses fulvous brown, dull or sublustrous, the margin rounded or tapering to an acute apex, sometimes a little prolonged and reflexed, the umbo inconspicuous.

A tree of the mountains of central, southern and western China with an outlying station on the Island of Formosa. Recently planted in Europe and America, it has so far proved hardy. The nuts are gathered for food and some use is made of the wood.

The glabrous shoots of P. Armandi distinguish it from P. flexilis and P. koraiensis. From the latter it is also distinct in its dehiscent cone and in its seed. The section of its leaf, with dorsal ducts often in two positions, is peculiar to this species among Soft Pines.

Plate IX.

Fig. 96, Two cones and seed. Fig. 97, Leaf-fascicle. Figs. 98, 99, Magnified sections of three leaves.



III. STROBI

Seed with a long effective wing adnate to the nut.

The base of the seed-wing corresponds to the marginal spermoderm of the Flexiles but is prolonged into an effective adnate wing. This form of wing appears again in the species Balfouriana and in the group Longifoliae.

Cones very long, usually exceeding 25 cm. Cone-scales prolonged and reflexed 6. ayacahuite. Cone-scales appressed 7. Lambertiana. Cones less than 25 cm. long. Cone-scales prominently convex. Leaves less than 7 cm. long 8. parviflora. Leaves 9-12 cm. long 9. peuce. Leaves 12-18 cm. long 10. excelsa. Cone-scales thin, conforming to the surface of the cone. Cone relatively longer, its phyllotaxis 8/21 11. monticola. Cone relatively shorter, its phyllotaxis 5/13 12. strobus.

6. PINUS AYACAHUITE

1838 P. ayacahuite Ehrenberg in Linnaea, xii. 492. 1848 P. strobiformis Engelmann in Wislizenus, Tour Mex. 102. 1857 P. Veitchii Roezl, Cat. Graines Conif. Mex. 32. 1858 P. Bonapartea Roezl in Gard. Chron. 358. 1858 P. Loudoniana Gordon, Pinet. 230.

Spring-shoots glabrous or pubescent. Leaves from 10 to 20 cm. long, serrulate, their stomata ventral only, their resin-ducts external, often numerous. Cones from 25 to 45 cm. long, pendent on long stalks, subcylindrical or tapering, often curved; apophyses pale nut-brown, dull or sublustrous, varying much in thickness, prolonged in various degrees, the prolongations patulous, reflexed, recurved or revolute; seeds of the southern typical form with a long wing, the wing diminishing and the nut increasing in relative size northward.

The White Pine of Mexico and Guatemala grows on mountain-slopes and at the head of ravines. It is not very hardy in cultivation except in the milder parts of Great Britain and in northern Italy, where the forms of central and northern Mexico have been very successful. The species is best recognized by the prolonged apophyses of its large cone.

The variations in the size of the cone and in the prolongations of its scales are many, but of far more significance is the remarkable variation of the seed-wing, which is long in the southern part of the range, short and broad in central Mexico, and rudimentary, like the seed of P. flexilis, in the north. This makes it possible to establish two well defined varieties—Veitchii and brachyptera. The three forms of the species present a gradation from the long effective wing of the Strobi to the rudimentary form of the Flexiles. Many of the seed-wings of the var. Veitchii correspond, in their short broad form and opaque coloring, with the characteristic wing of P. Lambertiana.

Plate X. (leaves and cones much reduced).

Fig. 103, Cone and cone-scale of var. Veitchii. Fig. 104, Cone and seed of var. brachyptera. Fig. 105, Cone-scale of the typical form. Figs. 106, 107, Leaf-fascicles and magnified leaf-sections.

7. PINUS LAMBERTIANA

1827 P. Lambertiana Douglas in Trans. Linn. Soc. xv. 497.

Spring-shoots pubescent. Leaves from 7 to 10 cm. long, serrulate; stomata dorsal and ventral; resin-ducts external or with one or two ventral medial ducts. Cones from 30 to 50 cm. long, pendent, subcylindrical, tapering to a rounded apex; apophyses pale nut-brown, thick, a narrow border of the under surface showing on the closed cone, the margin rounded or tapering to a blunt slightly reflexed tip; seed with a large nut and a broad short opaque wing.

The Sugar Pine is the tallest of the genus and attains a height of 50 or 60 metres. It grows on mountain slopes and the sides of ravines. Its southern limit is in Lower California on the plateau of San Pedro Martir, its northern limit is in western Oregon. The wood is valuable, its nuts are eaten by native Indians, and the sweet exudation, which gives the tree its popular name, is a manna-like substance of some officinal value. P. Lambertiana is recognized by its long cone and by the constant dorsal stomata of its leaves.

Plate X. (leaves and cone much reduced).

Fig. 100, Cone and seed. Fig. 101, Conelet. Fig. 102, Leaf-fascicle and magnified leaf-section.



8. PINUS PARVIFLORA

1784 P. cembra Thunberg, Fl. Jap. 274. (not Linnaeus). 1842 P. parviflora Siebold and Zuccarini, Fl. Jap. ii. 27, t. 115. 1890 P. pentaphylla Mayr, Mon. Abiet. Jap. 78, 94, t. 6. 1908 P. morrisonicola Hayata in Gard. Chron. ser. 3, xliii. 194. 1908 P. formosana Hayata in Jour. Linn. Soc. xxxviii. 297, t. 22.

Spring-shoots pubescent or glabrous; branches becoming studded with prominent resin-cells of the cortex. Leaves from 3 to 8 cm. long, slender, serrulate; stomata ventral only; resin-ducts external and dorsal. Cones subsessile, often persistent, from 5 to 10 cm. long, patulous or horizontal, short-ovate, or elongate and slightly conical; apophyses nut-brown, abruptly convex near the apex, or irregularly warped, varying much in size, the umbo confluent with the thin margin of the scale and resting on the apophysis beneath; seeds with a large nut and a short broad wing, often temporarily adherent to the cone-scale and breaking apart at the fall of the nut.

A tree of the mountains of Japan and Formosa, cultivated extensively. It is recognized by its very short quinate leaves and by its nearly sessile cones. The frequent but not invariable retention of the seed-wing in the cone is due to adhesion. Many seeds fall with their wings intact, others break away from the wing which, after a while, loosens and also falls.

Plate XI.

Figs. 114, 115, Three cones and seed. Fig. 116, Leaf-fascicle and magnified leaf-section.

9. PINUS PEUCE

1844 P. peuce Grisebach, Spicil. Fl. Rumel. ii. 349. 1865 P. excelsa Hooker in Jour. Linn. Soc. viii. 145. (not Wallich).

Spring-shoots glabrous. Leaves from 7 to 10 cm. long, erect, serrulate; stomata ventral only; resin-ducts external. Connective of pollen-sacs small and narrow. Cones deciduous, from 8 to 15 cm. long, subcylindrical, often curved, the peduncle short; apophyses tawny yellow, prominently and abruptly convex, the umbo against the scale beneath; seed-wing long.

A tree of the Balkan Mountains, very hardy and bearing abundant fruit in the gardens of both hemispheres. The cone resembles that of P. excelsa, but is prevalently much shorter and with a relatively shorter peduncle. Its leaves are also much shorter and are always erect. A curious difference is found in the connectives of the pollen-sacs, small in peuce (fig. 113), large in excelsa (fig. 110). The convexity of its apophyses distinguishes the cone from those of P. monticola and P. strobus. Beissner followed Hooker and named this species excelsa, var. peuce, in the first edition of his Handbuch (1891), but in the second edition he restored the Balkan Pine to specific standing.

Plate XI.

Fig. 111, Cone and seed. Fig. 112, Leaf-fascicle and magnified leaf-section. Fig. 113, Pollen-sacs and connective magnified.

10. PINUS EXCELSA

1824 P. excelsa Wallich ex Lambert, Gen. Pin. ii, 5, t. 3. 1845 P. nepalensis De Chambray, Arbr. Resin. 342. 1854 P. Griffithii McClelland in Griffith, Notul. Pl. Asiat. iv, 17; Icon. Pl. Asiat. t. 365.

Spring-shoots glabrous. Leaves from 10 to 18 cm. long, drooping, serrulate; stomata ventral only; resin-ducts external but often with a medial ventral duct. Connective of the pollen-sacs large. Cones from 15 to 25 cm. long, narrow-cylindrical; apophyses tawny yellow or pale fulvous brown, prominently convex, the umbo against the apophysis beneath; seeds with a long wing.

A tree with gray-green drooping foliage, found, with some interruptions, along the Himalayas. It furnishes resin, tar and wood of considerable value. It is cultivated in all temperate climates and is a familiar tree of American and European gardens. Madden states that the foliage of P. excelsa is sometimes erect and is occasionally bright green. Such variations are often met in other species of Pinus. Usually the drooping gray-green foliage and the peculiar cone are sufficient for the recognition of this species. The not infrequent presence of a medial duct and the large connective are valuable aids for identifying it.

Plate XI.

Fig. 108, Cone and seed. Fig. 109, Leaf-fascicle and magnified section of two leaves. Fig. 110, Pollen-sacs and connective magnified.



11. PINUS MONTICOLA

1837 P. monticola Douglas ex Lambert, Gen. Pin. iii. t. 1884 P. porphyrocarpa Lawson, Pinet. Brit. i, 83, ff.

Spring-shouts pubescent. Leaves from 4 to 10 cm. long, serrulate; stomata ventral or rarely with a few dorsal stomata; resin-ducts external. Cones from 10 to 25 cm. long, cylindrical or tapering, sometimes curved; apophyses brown-ochre or fulvous brown, thin, smooth, conforming to the surface of the cone, the apex sometimes slightly prolonged and reflexed, the umbo not quite touching the surface of the scale below.

The western White Pine grows in southern British Columbia and on Vancouver Island, on the Rocky Mountains of Montana and Idaho, in Washington, on the Blue Mountains, Cascades and Coast Range of Oregon, across northern California and along the Sierras to the mountains of southern California. Where it is abundant and accessible it furnishes valuable timber. It is hardy in New England and in northern and central Europe.

It differs from P. strobus in the higher phyllotaxis of its cone, an obvious difference that may be seen by comparing cones of the two species of the same length (figs. 117, 119), the number of scales on the cone of P. monticola being much greater than that on the cone of P. strobus. Nuttall (Sylva, iii, 118) followed Hooker in considering it to be a variety of P. strobus.

Plate XII.

Fig. 117, Cone and cone-scale. Fig. 118, Leaf-fascicle and magnified leaf-section.

12. PINUS STROBUS

1753 P. strobus Linnaeus, Sp. Pl. 1001. 1855 P. nivea Booth ex Carriere, Trait. Conif. 305. 1862 P. alba-canadensis Provancher, Fl. Canad. ii. 554. 1903 Strobus strobus Small, Fl. Southeast. U. S. 29.

Spring-shoots pubescent. Leaves from 6 to 14 cm. long, serrulate; stomata ventral only; resin-ducts external. Cones from 8 to 24 cm. long, narrow cylindrical, sometimes curved; apophyses fulvous brown, or rufous brown, thin, the smooth or slightly rugose surface conforming to the general surface of the cone; seed with a long wing.

A valuable timber-tree of singular beauty and rapid growth. The northern limit of its range extends from Newfoundland to Manitoba; it grows throughout the northern states from Minnesota to the Atlantic, and, south of Pennsylvania, along the Appalachians to northern Georgia. Its tractable and reliable wood, its adaptability to various soils and climates, its early maturity and stately habit, recommend it to the forester and gardener.

Mature trees of P. strobus tower above the evergreens associated with it. It is also recognized by the color and horizontal massing of its foliage. The cone, when closed, is very narrow; its thin flat scales distinguish it from the cone of P. peuce, and its phyllotaxis from the cone of P. monticola. To illustrate the possibilities of variation in the size of Pine cones, I once collected several in Tamworth, N. H., on the estate of Mr. Augustus Hemenway, on the same slope and within an area of one square kilometre. These cones varied in length from 6 to 24 cm., with all intermediate sizes. Also on each tree were cones of various lengths, but the longest were confined to two or three trees among the several hundred examined. Dimensions of leaves also varied with individual trees; not infrequently the leaves of a tree were twice the length of those of an adjacent tree. Such variations appear in many species and in many localities.

Plate XII.

Fig. 119, Two cones. Fig. 120, Leaf-fascicle. Fig. 121, Magnified leaf-section. Fig. 122, Conelets. Fig. 123, A cultivated tree in Massachusetts.



Paracembra

Umbo of the cone-scale dorsal. Scales of the conelet mucronate or aristate. Epiderm and hypoderm of the leaf similar, appearing as a single tissue; resin-ducts external. Pits of the ray-cells small.

The wood of this subsection differs from that of other species, except that of P. pinea, in the Picea-like characters of the medullary rays—tracheids with smooth walls combined with the thick walls and small pits of the ray-cells. On the character of the seeds the species may be divided into three groups.

Seeds wingless IV. Cembroides. Seeds with a short, ineffective, articulate wing V. Gerardianae. Seeds with a long and effective wing VI. Balfourianae.

IV. CEMBROIDES

Seeds wingless, the nut large, wholly or partly bare of membranous cover. Cones varying from yellow-ochre to deep red-orange in color.

These are the Nut Pines, growing on the arid slopes and table-lands above the great plateau of northern Mexico and its extension into the southwestern United States. There are three distinct species.

Leaves entire, the sheath deciduous. Cones subglobose, subsessile 13. cembroides. Cones cylindrical, pedunculate 14. Pinceana. Leaves serrulate, the sheath persistent 15. Nelsonii.

13. PINUS CEMBROIDES

1832 P. cembroides Zuccarini in Abh. Akad. Muench. i. 392. 1838 P. Llaveana Schiede in Linnaea, xii. 488. 1845 P. monophylla Torrey in Fremont's Rep. 319, t. 4. 1847 P. Fremontiana Endlicher, Syn. Conif. 183. 1848 P. edulis Engelmann in Wislizenus, Tour. Mex. 88. 1848 P. osteosperma Engelmann in Wislizenus, Tour. Mex. 89. 1862 P. Parryana Engelmann in Am. Jour. Sci. ser. 2, xxxiv. 332 (not Gordon). 1897 P. quadrifolia Sudworth, Bull. 14, U. S. Dep. Agric. 17. 1903 Caryopitys edulus Small, Fl. Southeast. U. S. 29.

Spring-shoots pruinose. Leaves from 2 to 6 cm. long, in fascicles of 1 to 5, the sheath-scales revolute at the apex, then deciduous; stomata ventral, or ventral and dorsal; resin-ducts external. Scales of the conelet armed with a minute prickle. Cones from 4 to 6 cm. long, subglobose, subsessile; apophyses lustrous ochre-yellow, crowned with a quadrilateral umbo bearing the minute prickle of the conelet; seed flaxen yellow when fresh, its testa bare, the spermoderm adnate to the cone-scale.

A broad tree with a round head, similar in size and form, but not in ramification, to the cultivated Apple-tree; growing on arid slopes and table-lands. Its eastern limit is in southwestern Wyoming, central Colorado, Texas, western Tamaulipas and northwestern Vera Cruz. It ranges over Utah, Nevada, Arizona and the northern states of Mexico to the southern Sierras of California and to the northern and southern extremities of Lower California. It is recognized by its small cone, which expands, when open, into an irregular flat aggregate of loosely attached scales. The leaves are shorter than those of the other Pines of this group.

The cone of this species always retains its peculiar character. The variations are mainly in the number of leaves in the fascicle. On this character this Nut Pine is divided by many authors into four species—cembroides, with three slender leaves—edulis, with two stout leaves—monophylla, with one leaf and—Parryana, with four stout leaves. But there are intermediate forms that may be either cembroides or edulis, edulis or monophylla etc., and Voss's reduction of the four to a single species with three varieties seems to be justified (Mitt. Deutsch. Dendrol. Ges. xvi. 95).

Plate XIII.

Fig. 130, Cone, cone-scale and seed. Fig. 131, Open cone. Fig. 132, Branchlet with leaves and magnified leaf-section.

14. PINUS PINCEANA

1846 P. cembroides Gordon in Jour. Hort. Soc. Lond. i. 236, f. (not Zuccarini). 1858 P. Pinceana Gordon, Pinet. 204. 1882 P. latisquama Engelmann in Gard. Chron. ser. 2, xviii. 712. f. 125 (as to cone only).

Spring-shoots slender, pruinose. Leaves in fascicles of three, the sheath revolute at the base, then deciduous; stomata ventral, or ventral and dorsal; resin-ducts external. Scales of the conelet minutely mucronate. Cones from 6 to 9 cm. long, cylindrical, pendent on long peduncles; apophyses lustrous ochre-yellow, elevated in the centre, the umbo usually retaining the small prickle; seed large, bearing on its dorsal surface remnants of the spermoderm.

A small bushy tree with long slender branchlets, clear gray cortex, persistently smooth except on the lower part of the trunk, and glaucous-green foliage. It grows along water-courses, dry in autumn and winter, from southern Coahuila to central Hidalgo, and is associated with P. cembroides, from which it may be distinguished by its longer leaves and much longer cylindrical cone.

Plate XIII.

Fig. 127, Cone, cone-scale and seed. Fig. 128, Branchlet with leaves. Fig. 129, Magnified leaf-section.

15. PINUS NELSONII

1904 P. Nelsonii Shaw in Gard. Chron. ser. 3, xxxvi. 122, f. 49.

Spring-shoots slender, pruinose; branchlets very pliant and tough, summer-shoots abundant. Leaves with a persistent sheath, from 6 to 9 cm. long, united in threes along a portion of their ventral surface into pseudomonophyllous fascicles, serrulate on the two margins of the dorsal surface, entire on the ventral margin; stomata dorsal and with one row along the free portion of each ventral face. Conelets usually, if not always, pseudolateral by reason of the summer growth of the branchlets, and attaining in their first season an unusually large size. Cones from 6 to 12 cm. long, on very long stout and curved peduncles, cylindrical, deciduous by an articulation between the cone and its peduncle, leaving the latter for several years on the tree; apophyses dark lustrous orange-red, rugose, elevated along a sharp transverse keel, the umbo obscurely defined, the mucro usually broken away; nuts large, flaxen yellow, the spermoderm adnate to the cone-scale.

A small bushy tree with long pliant branches, clear gray cortex all over the limbs and trunk, and sparse gray-green foliage. It grows, together with P. cembroides, on the lower slopes of the northeastern Sierras of Mexico, near the boundary between the states of Tamaulipas and Nuevo Leon. It is apparently confined to a small area near the latitude of the city of Victoria, the capital of Tamaulipas, where its nuts are often exposed for sale.

In many characters this species is unique. It can be recognized at once by the connate leaves that form the fascicle or by the remarkable stout curved peduncle of its cone. Such seeds as I have seen differ from those of P. cembroides by a reddish area at one end, but this can be seen with fresh seeds only.

Plate XIII.

Fig. 124, Cone, cone scale and seed. Fig. 125, Branchlet with leaves. Fig. 126, Magnified section of a leaf-fascicle.



V. GERARDIANAE

Seeds with a very short ineffective articulate wing. Leaves in fascicles of 3, serrulate, the sheath deciduous. Bark exfoliating in large scales, leaving parti-colored areas.

These Asiatic Nut Pines are alike in leaf and cortex as well as in the peculiar seed-wing. The last often remains in the cone after the nut falls. The mechanical nature of this adhesion is apparent in P. Gerardiana, where the wing adheres not to its own, but to the adjacent scale. The two species are alike in their leaves but distinct in their cones and seeds.

Cones smaller, the nut short-ovate 16. Bungeana. Cones larger, the nut long-cylindrical 17. Gerardiana.

16. PINUS BUNGEANA

1847 P. Bungeana Zuccarini ex Endlicher, Syn. Conif. 166.

Spring-shoots glabrous, summer-shoots common on fruiting branches of young trees. Leaves from 6 to 10 cm. long, serrulate; stomata dorsal and ventral; resin-ducts external. Conelets subterminal or often pseudolateral, their scales gradually narrowed into a spine. Cones from 5 to 7 cm. long, short-pedunculate, short-ovate; apophyses dull pale nut-brown, elevated along a transverse keel, the dark brown umbo forming a spine with a broad base; seeds with a short loosely attached wing, sometimes remaining in the cone when the short-ovate nut falls.

A tree cultivated about the temples of China and recently found by Wilson growing on the mountains of Hupeh. The earlier parti-colored bark changes to chalky white on old trunks, by which the tree is recognized from a great distance. The stem of the tree is often multiple by the vertical growth of some of the lower branches. It is very hardy and is cultivated in Europe and America, although these cultivated trees are not yet of sufficient age to show the remarkable white trunk.

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