234 GYMNOSPERMS 



reproductive structures, especially the gametophytes and early 

 embryogeny. Anatomists have studied, almost exclusively, the 

 adult structures, with scant attention to the origin and development 

 of the vascular system. The valuable results secured by vertebrate 

 paleontologists, working almost entirely with bones, have led anat- 

 omists to assume that the woody structures of plants are equally 

 reliable in tracing phylogeny. A study of ecological anatomy shows 

 that woody structures are quite susceptible to changes in conditions; 

 while phylogenetic anatomy indicates that some features of the 

 vascular system keep their characters in spite of changed environ- 

 ment. These remarks are intended to apply not to sudden ephemeral 

 changes in environment, but to such changes as bring about extinc- 

 tion or modification of a species, genus, or order. 



THE SPOROPHYTE —VEGETATIVE 



The Coniferales are characteristically trees with evergreen leaves, 

 very few, like some species of Juniperus, being small enough and 

 diffuse enough to be ranked as shrubs. There are no herbaceous 

 forms. 



The stem. — The usual growth of the stem is strongly spiral, re- 

 sulting in the typically pyramidal form of the tree. But diffuse 

 branching is also common, the strong apical growth being lost, so 

 that it is impossible to determine what is the main axis and what 

 may be branches, as in Pinus torrcyana, Taxodium mucronatum, 

 Cupressus macrocarpa, and Juniperus monosperma (figs. 242, and 



239)- 



In Pinus sabiniana the stem is often, perhaps usually, dichot- 



omously branched (fig. 243). It is not hard to find trees of other 

 genera in which there is dichotomy, as in Ptcridophytes. A single 

 dichotomy is very widespread in the order. I have personally ob- 

 served it in more than 20 genera. 



Many of the conifers are extremely endemic. Probably the great- 

 est extreme in endemism in the entire gymnosperm phylum can be 

 seen along the western coast of California, from the Monterey- 

 Carmel region southward. In the Monterey-Carmel region, four 

 endemic species can be found in an hour's walking, Cupressus ma- 

 crocarpa, C. goweniana, Pinus radiaia, and P. muricata (fig. 244). 



