Abstract
The most important factors determining tree growth in various climates are inherited differences in the germ plasma. Each tree species has its own tree line, and some have evolved low elfin-wood races beyond the tree limits. The most widely distributed trees belong to species complexes that are known for their ability to hybridize. The tolerance groups of trees follow major systematic orders. These are based on morphological characters, which apparently are associated with physiological characters of adaptive importance.

This publication has 2 references indexed in Scilit: