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.