167] ENGELMANN—REVISION OF THE GENUS PINUS, ETC. 7 
may be relied on to some extent for diagnostic purposes. Thus 
the quinate smooth-edged leaves of P. flexilis and P. Balfour- 
tana, which would be difficult to distinguish without their cones, 
may be readily recognized by the strengthening cells, which in 
the latter surround the more closely approximating ducts, while 
in the former the ducts, widely apart from one another, are desti- 
tute of these cells. 
€ PERSISTENCE of the leaves is very different in different 
species; in P. Strodus and others they fall in the autumn of the 
second year; more commonly they last to the end of the third 
year; in some species, e.g. P. Banksiana, they do not fall before 
they are 4, 5 or even 6 years old; in P. Balfourtana, or at least 
in var. arzstata, I have seen them persist 12 to 14 years. en 
the leaves persist only a short time and are long, and the annual 
growth of the axis is short, they form brushes or tassels (P. aus- 
tralis) at the end of the branchlets, but where they are short and 
persist long (P. Balfouriana) they give the branchlets that “‘fox- 
tail or bottle-brush” appearance of which travellers speak. In 
young and vigorous trees the leaves are apt to persist longer than 
in old ones. 
In exceptional cases and as a monstrosity the leaf-bundles be- 
come proliferous, the branchlet which bears the secondary leaves 
elongating and forming a regular branch. 
The pines are moneecious trees which bear their male and fe- 
male flowers generally on different branchlets, the male commonly 
on the lower, the female frequently on the upper part of the tree ; 
sometimes both are found on the same axis, the male below, the 
female above. 
The MALE FLOWERS are borne on the lowest part of the year’s 
shoot, in the axil of bracts, either crowded together in a kind of 
a head or elongated in a spike; the axis usually continues to 
elongate during or after flowering and makes a leafy branch, 
which in its continuation in succeeding years often again bears 
flowers. Male flowers sometimes abnormally make their appear- 
ance higher up.on the axis mixed with leaf-bundles and occupy- 
ing the place of such. The male flowers consist of an indefinite 
number of anthers sessile on a more or less elongated column, 
and have the form of an oval or a cylindrical ament, for which 
they used to be taken. They are surrounded by a somewhat defi- 
