ENGELMANN — REVISION OF THE GENUS PINUS, ETC. 167 



may be relied on to some extent for diagnostic purposes. Thus 

 the quinate smooth-edged leaves of P. Jlexilis and P. Balfozir- 

 zana, 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. 



The PERSISTENCE of the leaves is very different in diflerent 

 species ; in P. Strobus 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. Balfoui'iana^ or at least 

 in var. arzstata, I have seen them persist 12 to 14 years. When 

 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. Balfotiriand) 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 j^ersist 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 monoecious 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 inale 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- 



