436 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 8 



progenies. The very fact that timber trees are longer lived than 

 agricultural crops is a distinct advantage, for it makes possible a 

 long-continued supply of better seeds once the desirable seed-trees 

 are found. Many of these superior trees that are being discovered 

 as the investigations progress have been growing for 100 years or 

 more, and are capable of yielding for many decades heavy seed crops 

 every few years. Even a single seed crop from one of these selected 

 seed-trees will often be such that enough seed can be collected to 

 produce from 5,000 to 20,000 superior seedlings. This illustrates the 

 untold potentialities of these new genetical methods, and the com- 

 paratively short time required for them to yield results that have 

 practical application to present-day reforestation. 



Results so far seem to indicate that the easily obtained wind-polli- 

 nated seed is usually adequate for the various preliminary tests in 

 which seed is gathered over wide areas, even though only one parent 

 is thus known and controlled. However, as the investigations become 

 localized in the areas that are found to contain the better trees, it 

 may prove desirable to conduct some of the progeny tests with self- 

 pollinated seed. Also, various tests of crossing the better individuals 

 will be helpful in showing which combinations of parents will yield the 

 best offspring. 



As rapidly as relatively isolated plots of native trees containing a 

 number of germinally superior individuals are found, it would seem 

 that in preparing them to serve as future seed supply areas, it may be 

 possible to improve the average vigor of the offspring from the best 

 trees still further by cutting out, not those that appear externally to 

 be undesirable, but those trees that the progeny tests have shown to 

 be inferior. Thus their pollen will be eliminated and henceforth 

 natural cross pollination will take place largely between the hereditarily 

 better types. 



The application of this progeny test method over a wide range of 

 seed sources has not only pointed out some of the best individual 

 seed-trees in each locality, but it has also brought to light marked 

 differences in the general character of the numerous local strains. In 

 one such test with ponderosa pine, the Institute compared side by 

 side in a single nursery the progenies of 765 individual seed-trees 

 growing in 60 counties hi 12 western States and in British Columbia. 

 The data gathered from this exhaustive study revealed the existence 

 of numerous geographical races of this important timber species, 

 each with distinct physical characteristics that will affect both the 

 volume and quality of the lumber produced. One of the most signifi- 

 cant and useful of the facts that these tests have revealed is that, in the 

 Sierra Nevada of California, hereditary vigor has been found to be 

 quite generally associated with the lower elevation of the seed source. 



