TREES AND SHRUBS 163 



corresponding variations in cypress and other 

 conifers grown from the seed. 



The Douglas spruce is a common California 

 form that is quite variable. This has excep- 

 tional interest, because it is a tree of very rapid 

 growth. In many cases where a tract of land 

 has been burned over or the trees have been cut 

 off, there will spring up what at first appears to 

 be a growth of oaks alone. But in fifteen or 

 twenty years the growth of Douglas spruce 

 will entirely overshadow the oaks, ultimately 

 destroying them altogether, and presenting yet 

 another illustration of the practical operation 

 of natural selection. 



But there is a very great variation among the 

 individuals of the different species of conifers as 

 to rapidity of growth. So there is fine oppor- 

 tunity for the experimenter to select the more 

 rapid-growing trees, and thus to develop a race 

 of timber trees of very exceptional value. 



The experiment is not difficult with the Doug- 

 las spruce (A. Douglasi) as it bears seed while 

 quite young, particularly when the trees stand 

 by themselves. The seed remains in the cones 

 for some time, to mature so that it may be col- 

 lected at any season of the year. The seeds ger- 

 minate readily, the seedlings may be easily trans- 

 planted, and in general this is one of the easiest 



