aos 



AMERICAN FOREST TREES 



hybrid a cross between highland oak and California black oak. It was first found 

 in 1863, and a considerable range has since been established for it. 



It is the opinion of some investigators that new tree species have their ori- 

 gin in crosses between existing species. Of the countless thousands of such 

 crosses a few, at long intervals of time, may develop characteristics which enable 

 them to maintain their existence and to spread into new territory. If that occurs, 

 a new kind of tree has appeared on earth and is ready to take its place among 

 the established forests of the region. Cross-fertilization among trees and plants 

 is very common, but so many adverse conditions are encountered, that few hy- 

 brids ever amount to anything, 



