Seed-Plants 141 



conifers, being very frequently gregarious in habit, 

 may form almost perfectly pure forests of a single 

 species. 



The most obvious difference between cycads and 

 conifers is the different relation of stem and leaves, 

 the same that distinguishes the ferns and club- 

 mosses. The simple, or sparingly branching palm- 

 like trunk of the cycads, with its crown of fern-like 

 fronds, is extremely different from the extensively 

 branched conifer, with its scattered, slender, and 

 often needle-shaped leaves. Most of the more fa- 

 miliar conifers, like the pines and firs, are more or 

 less markedly xerophytic, i.e., their foliage is 

 adapted to check excessive transpiration. This may 

 be correlated with their growth in dry regions 

 where they are exposed to the hot sun, or it may 

 be in the case of the Northern species an adaptation 

 to prevent loss of water during the winter, a con- 

 dition which the Northern angiospermous trees meet 

 by casting their leaves. Species growing in moister 

 regions have softer and broader leaves, and this is 

 noticeably the case in some of the presumably more 

 primitive types, like Araucaria and the Kauri pine 

 of New Zealand, which have relatively broad leaves 

 and are decidedly less xerophytic in habit than the 

 pines and spruces of the North. While most of the 

 conifers are evergreens, a few, like the larch, and 

 the bald cypress of the Gulf region, cast their leaves 

 in autumn, behaving thus like deciduous angio- 

 spermous trees. 



