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Read Ebook: The Genus Pinus by Shaw George Russell Shaw George Russell Illustrator
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Ebook has 495 lines and 44038 words, and 10 pages
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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
Cone 8 IV
Phyllotaxis 12 V
Cone-tissues and Seeds 12-16 VI
Bark 18
PART 2 CLASSIFICATION OF THE SPECIES 22
Sections, subsections and groups 25
Section Haploxylon 26
Subsection Cembra 26
Group Cembrae 26
Group Flexiles 28
Group Strobi 30
Pinus Ayacahuite, Lambertiana 30, 32 X
Subsection Paracembra 36
Group Cembroides 38
Group Gerardianae 40
Group Balfourianae 42
Section Diploxylon 44
Subsection Parapinaster 44
Group Leiophyllae 44
Group Longifoliae 46
Group Pineae 48
Subsection Pinaster 50
Group Laricionea 51
Massoniana, Densiflora 52 XX
Group Australes 62
Taeda, Glabra, Echinata 72, 74 XXX
Group Insignes 76
Group Macrocarpae 90
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 . 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 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.
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 are not apparent without removing the bud-scales, but, with most Hard Pines, they form enlargements of the bud .
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 . The latter develop into shoots in the centre of a leaf-fascicle when the branchlet, bearing the fascicle, has been injured.
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