yO 
OF THE GENUS PINUS. 563 
persistent and very numerous in each tuft, whilst in the Larches 
the leaves are equally numerous, but deciduous. The male 
flowers of Cedars and Larches are, moreover, solitary, not 
clustered. ; 
Whilst the genus is readily recognizable, it is often far otherwise 
with the species. It is not even easy to group them satisfac- 
torily into subgenera and sections. Reference to the standard 
text-books of Lambert, Endlicher, Parlatore, Engelmann, Gordon, 
Carri¢re, Beissner, Kent, and others, will suffice to show the 
correctness of this assertion. 
The most recent attempt to deal with the whole of the species 
is that of Engelmann, in the Transactions of the Academy of 
Sciences of St. Louis, iv. p. 161 (February 1880). Beissner, 
‘ Handbuch der Nadelholzkunde’ (1891), p. 209 ; Sargent, ‘Silva,’ 
vol. xi. (1897); Kent in Veitch’s Manual, ed. 2 (1900), p. 308, 
not to speak of others, have given their attention to certain 
species only, and not to the whole number, and they have, for 
the most part, followed Engelmann’s arrangement. This is 
noteworthy for several reasons, to some of which allusion may 
here be made. In the first place, even Engelmann’s Revision 
is not complete. It deals with sections and subsections, and 
with various minor subdivisions, but does not extend to the 
individual species, which are merely named under the sub- 
division to which they respectively belong. 
Histonogical CHARACTERS. 
In the next place, Engelmann makes use, for systematic 
purposes, of the position within the leaf of the resin-canals, 
whether marginal, 7. e. ‘‘ peripheral,” or just beneath the epi- 
dermis (Pl. 20. fig. 1); “ parenchymatous,” or in the substance 
ot the leaf (PI. 20. fig. 2); or *‘ internal,” when they are placed in 
juxtaposition to the endoderm (Pl. 20. fig. 3). Engelmann also 
lays some stress on the circumstance of the resin-canals being 
surrounded by “strengthening cells” (PI. 20. figs. 1 & 2) or 
devoid of any such investment. 
Koehne, in his ‘Deutsche Dendrologie’ (1893), p. 28, makes 
further use of histological characters by dividing the genus into 
two sections—* Haploxylon,” in which the central fibro-vascular 
bundle is simple (Pl. 20. fig.2); and “ Diploxylon,” in which the 
bundle branches into two divisions which are more or less closely 
approximate or separated by cellular tissue or stereome-celis 
