362 REVISION OF THE GENUS PINUS. 
branchlet in the axils of primary leaves or paged of bracts, and are surrounded at base by a sheath 
of bud-scales (Wiederblaetter). These consist of 2 short, rigid, strongly keeled, lateral bracts and a 
number (6-10 or more) of longer, thinner inner ones, which generally are woven together by the deli- 
cate fringes of their edges, and are then persistent with the leaves, though in time worn off at the 
ends; or they are loose, at last spreading and deciduous at the end of the first season. This is the 
case in all the species of the section Strvbus, in the nut-pines, and in a few others: P. Balfouriana, 
Gerardiana, Bungeona, Chihuahuana, and usually also in P. ee 
The secondary leaves generally occur in definite numbers, 1 to 5, in a bunch, or their number is 
slightly variable: some species have regularly 2 and 3 leaves (P. te P. Hiliottit), others vary with 
3 to 5 leaves (P. Montezume) ; species with regularly 3 leaves have occasionally 2 or 4, such with 5 
leaves are sometimes found with 6 and even 7 leaves. Where we have one (only in P. monophylla), 
the leaf is terete ; where there are two, the leaves are semi-terete, convex on the lower surface and flat 
on the upper one when fresh, or channelled when dry. Those leaves that grow in bundles of 3 or 
more are triangular, the upper surface being more or less elevated and keeled; ternate leaves are 
generally somewhat flatter, and quinate ones higher and regularly triangular. Thus the shape of the 
leaf and especially its transverse section is mostly sufficient to determine the number in which they 
occur. 
The leaves are in most species minutely but sharply serrulate on the edges, and mostly also on 
the keel of the upper surface. These serratures are closer together, or more distant, coarser or more 
delicate, but are absent only in a very few West-American species : the cembroid or nut-pines, P. Bal- 
fouriana, and most forms of P. jlexilis. The tips of the leaves are generally entire, acute, or acumi- 
nate, rarely obtusish ; but in all the species of the section Strobus they are in the young and fresh 
leaves finely denticulate. 
The stomata are usually distributed in longitudinal rows over both surfaces in the Pinaster [165] 
section; only P. Balfouriana has none on the back, and thus approaches Strobus in this as it 
does in many other respects. In Strobus we find on the back no or but few stomata, or sometimes a 
_ single or an interrupted line of them. P. Lambertiana only has numerous stomata on the back, thus 
approaching Pinaster. 
I will have to dwell somewhat extensively on the internal structure of the leaves, as it proves 
to be of the greatest importance for the classification of the species. We distinguish in a transverse 
section the thick epidermis, the chlorophyll-bearing parenchyma cells, and in the centre the fibro- 
vascular bundle. This latter is single in the terete and mostly in the quinate leaves ; it is double 
in the broader triangular or ternate, and in the semi-terete or binate leaves. This difference, how- 
ever, is of very little diagnostic importance, as we find occasionally single or double bundles in the 
same species. The fibro-vascular bundles always show wood cells on the upper or ventral, and bast 
cells on the lower or dorsal side, traversed by delicate medullary rays, usually obliquely diverging 
from the lower to the upper side. The bundles are imbedded in a mass of small (medullary 2?) cells, 
free of chlorophyll, and are together with those surrounded and separated from the parenchyma by 
a sheath of larger cells, also destitute of chlorophyll. 
Within the parenchyma of the leaf a smaller or larger number of longitudinal tubes or ducts 
are found, the RESIN-DUCTS, normally probably two, but very often more, even as many as a dozen 
or more. These ducts occupy a certain definite position within the leaf. They lie (1) close to the 
epidermis, peripheral ducts, in some species more on the ventral, in others more on the dorsal side of 
the leaf; or (2) they occupy a place within the parenchyma and surrounded by it on all sides, par- 
enchymatous ducts ; or (3) they lie close to the sheath which surrounds the vascular bundles, internal 
ducts. This position of the ducts is so constant, and seems to be so intimately connected with the 
essential character of the plant, that I venture to adopt it as one of the principal characters for the 
subdivision of the genus. I must add, however, that in some few species smaller, accessory ducts do 
