HYBRIDS 125 



once which ones are to be valuable he may hurry the 

 process by grafting a large number of cuttings from 

 young hybrid seedlings into the tops of larger 

 trees which are already bearing but cut back for top- 

 working. It is possible to put one hundred or more 

 seedlings in the top of some one stock tree at one 

 time, labeling each one, and in this way avoid several 

 years of waiting to see what is coming out of a lot 

 of young seedling hybrids. The latter, with only 

 part of the top cut off, keep right on growing, so 

 nothing is lost. 



The flowering time of different trees varies con- 

 siderably. For that reason it is well to have varieties 

 of species which blossom at the same time within 

 easy hailing distance of each other so that they may 

 exchange the gold pieces of their pollen. Many of 

 the Persian walnuts, like many other trees which 

 have been long under cultivation are not self -pol- 

 linating or if self -pollinating do not respond with 

 enthusiasm to close inbreeding. They require some 

 neighboring tree to furnish the most stimulating 

 pollen. This is true also of some of our best pecans. 

 With them it can hardly be a matter of long culti- 

 vation but rather a fact indicating that a very fine 

 variety, fine from man's point of view, is not in the 

 list of Nature's favorites. Nature is indifferent about 

 continuing the propagation of kinds of which she 

 does not fully approve. There is another biologic 

 law involved. We find a parallel with animals. The 

 American bison which lived in large herds seemed 

 to require crossing over a large number for success- 



