258 BOTANICAL GAZETTE. [Oct., 
The number of species of American pines, exclusive of Mexico, 
as given by Prof. C. S. Sargent, in the tenth census report, is 
thirty-five. These have all been examined, as well as eight or 
ten Mexican species, which are also included. The material has 
been obtained from the Harvard herbarium, from other well known 
herbaria, and also from the very instructive slides prepared by the 
Rev. J. D. King, whose material was obtained from Prof. Sargent. 
Effort was made to obtain material from as wide a range as pos- 
sible, and repeated studies of the same forms were constantly made. 
ransverse sections of the leaf are used, and these should al- 
ways be made well away from either its base or apex. Neglect 
of this precaution has led to confusion, as a leaf with two distinet 
fibro-vascular bundles, may be thought to have but one if the sec- 
tion is made near the extremities. ‘The bundles usually separate 
above the base of the leaf, and blend again near its apex, and in 
poorly developed leaves may never appear separate at all. This 
led Dr. Engelmann to say that the single or double bundle s 
of very little diagnostic importance, as we find occasionally single 
or double bundles in the same species,”' while, with the precau- 
tion mentioned, we have known it to fail but once. 
he outline ofa transverse section, in the main, depends upon 
the number of leaves in a fascicle, but this can not be pressed too 
far. In P. monophylla the outline is nearly circular, in 2-leaved 
species it is semicircular, in 3-leaved species triangular, but in 
5-leaved species it is also triangular. It is thus usually possible 
to determine approximately the number of leaves in a fasicle by 
the transverse section of a single one,and hence the number of 
leaves will also be legitimately included among our anatomical 
characters. ; 
The leaf-structure is separable into three regions, the cortical, 
the mesophyll and the fibro-vascular. j 
€ cortical region. This is composed of one layer of epi- 
dermal cells, with very thick walls, interrupted here and there by 
stomata. The position and number of rows of stomata are = 
uable characters. In some species, as P, Strobus, they are foun 
only on the ventral side; in others, as in P. Coulteri, they occur 
both dorsally and ventrally. The rest of the cortical region is made 
up of the so-called “ hypoderma,” being mostly very thick-walled 
cells, aptly called by Engelmann “ strengthening cells” Engel 
mann rejected the term “hypoderma,” because cells of the same Da- 
ture often occur About the resin ducts and in the fibro-vascular re- 
gion. Theterm “strengthening cells,” therefore refers to this thick- 
walled tissue wherever found, and they may be cortical, about the 
'Trans. St. Louis Acad., iv. 165, 
