s 
342 A SYNOPSIS OF THE AMERICAN FIRS. 
ject in 1874, in Ann. Sci. Nat. Bot., 20, pp. 5-153, with 12 plates. He was followed in the 
succeeding year by W. R. McNab in Proce. Ivish Acad., 2, pp. 209-213, with 1 plate; and in [594 (2)]} 
1877 the same published an exhaustive paper in the same Journal, pp. 673-704, with 4 
plates. E. Purkinje, of the Foresters’ Academy of Weisswasser in Austria, made, four or five years 
ago, extensive investigations on the same subject, but has, I believe, not yet given his results to the 
public. My own studies in this line, commenced some fifteen years ago, when the conifers of the 
Rocky Mountains first got into the hands of botanists, have been carried on more assiduously within 
the last three years. 
Highly important as the microscopic investigations of the leaf anatomy are, they have sometimes 
been relied on too exclusively, disregarding the characters furnished by the reproductive organs.? 
It may not be useless to repeat that the leaves of all firs are sessile with a circular base (leaving 
a circular scar in falling off), and without the prominent persistent ligneous cushion which is peculiar 
to the spruces. They are usually more or less flattened, grooved above and keeled below, and those of 
the branches are mostly twisted above the base so as to give them a more or less distichous direction ; 
the leaves of the erect shoots are thicker and convex above, and not twisted. The tip of the leaves 
of young trees, and of the lower branches of older ones, is notched in almost all species ; the leaves of 
robust shoots and of fertile branches are mostly entire, obtuse in some, acute in others? All the 
leaves have stomata on the under side, arranged in a smaller or larger number of series, forming 
bands on each side of the keel. On the upper side of the leaf stomata are present in some, especially 
in those with thicker leaves, and absent in other species, mostly in those with flatter leaves; in sev- 
eral species the leaves of the lower or sterile branches are without stomata above, and the thicker 
ones of the upper or fertile branches have a few (in the upper part of the groove) or many. The 
thick epidermis of the upper surface is mostly underlaid and strengthened by very robust 
longitudinal cells, with thick walls and a very slender cavity, which have been named [595 (3)] 
pseudo-bast cells, but are now generally known as hypoderm cells. They are almost always 
present on the edges and the keel of the leaf, there sometimes crowded in 3-5 layers, and they often 
form a more or less interrupted stratum on the upper side. Where stomata pierce the epidermis, the 
hypodermic stratum is incomplete, or entirely absent. Only in a few species (A. bracteata and relt- 
giosa and the Asiatic firma) we find such cells also in the interior of the leaf, a case which is com- 
mon in true pines. In some species the diameter of these cells is equal to that of the epidermis 
cells ; in some it is smaller, and in a very few larger. Their presence, distribution, and relative size 
is tolerably constant, and furnishes good specific chusacte 
I do not describe the parenchymatous cells containing chlotophy’. nor their variety the so-called - 
palisade cells (elongated cells perpendicular to the upper side of the leaf), as no essential characters 
are derived from them. But of great diagnostic importance are the resin-ducts, of which there are 
always two in the Abies leaf, readily seen in a horizontal section. In some species they are placed 
on the lower side of the leaf, close to the epidermis and mostly near the edges; in others we find 
them in the parenchyma, about equidistant from the upper and lower surface. 
The fibro-vascular bundle occupies the centre of the leaf, either single (in the more square leaves 
of the 4th section), or mostly divided in two distinct bundles (in the flat leaves). Both cases occur 
sometimes in the same species. The bundles show the larger (ligneous) cells above and the smaller 
(bast-) cells below; they are surrounded by small pith-like cells, -— the whole separated from the 
snore by a sheath of larger cells. 
The separation by Bertrand, followed by McNab, of 
ae nobilis from the other firs, and the connecting it with 
Pseudotsuga Douglasii, notwithstanding their striking dif- 
ust be considered as the 
the necessity of collecting, if possible, branches 
of a young tree, erect shoots, lower branches of older, fertile 
trees (the only specimens which we usually find in Herbaria, 
because easily attainable) and branches with male and such 
with female fowers, or with their vestiges ; besides these, the 
cones and seeds and young seedling plants are important. A 
slice of the bark of old and of young trees ought to complete 
