Figs. 208, 209, Three cones. Fig. 210, Leaf-fascicle and magnified leaf-section.
XI. AUSTRALES
Pits of the ray-cells small. Leaf-hypoderm biform or variable. Spring-shoots uninodal in some, multinodal in other species. Cones dehiscent at maturity.
This group combines the dehiscent cone of the Lariciones with the wood-anatomy of the serotinous Pines. Also the multinodal spring-shoot first appears here and is gradually developed among the species, absent in Nos. 37-39, sometimes present in Nos. 40-43, and prevalent in Nos. 44-47.
All the species are of the Western Hemisphere, and among them may be found the biform hypoderm of the leaf, the internal resin-duct, and the total absence of external resin-ducts, characters common in American Hard Pines. The eastern species are quite constant in their characters and present no varietal forms; the western species, on the other hand, are very variable. This difference may be due to the even level and slight climatic differences of the Atlantic states and to the remarkable diversity of altitude and climate of the western states and Mexico.