438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



countries for hybridization with native species and with others that 

 may be flowering in the arboretum. 



The possibility of hybridizing forest trees, and of actually combin- 

 ing in a single new hybrid form the desirable characters previously 

 existing only in separate species, has been fully demonstrated in 

 hybrids produced at the Institute, as well as in certain natural hybrids 

 that have been discovered. The most outstanding of the Institute's 

 artificial hybrids to date is a cross of the Knobcone pine, Pinus atten- 

 uata, a relatively slow-growing but hardy species, and the Monterey 

 pine, Pinus radiata, a species which lacks hardiness but which is the 

 fastest-growing of all species tested from 40 countries. All of the 

 hybrids have, very fortunately, inherited the cold-hardiness of the 

 seed-parent and the rapid growth of the pollen-parent. 



As one of the results of the study of artificially controlled pollina- 

 tion of pines, it has been observed in experiments with several different 

 species that when the flowers of a pine tree are pollinated with pollen 

 from the same tree, the yield of seed tends to be abnormally low, and 

 the germination of the seeds is usually comparatively poor. In addi- 

 tion, the resultant seedlings are often quite deficient in vigor, as com- 

 pared with normal seedlings resulting from wind-pollination, which 

 ordinarily seems to include much crossing with neighboring trees. 

 These results may be taken as indications that, in all probability, 

 many of the individual trees in the wilds are partially self-sterile and 

 will yield vigorous offspring only when cross-pollinated with pollen 

 from other trees, usually of the same species. 



Apparently pines behave much as do many of the crop plants, such 

 as corn, that have been under tests by geneticists for decades. It is 

 a common experience in plant breeding to find that there is a reduc- 

 tion in vigor following selling or inbreeding, particularly in the first 

 generation. One application of this finding in practical forestry is to 

 avoid the collection of seeds from individual trees that are compara- 

 tively isolated, since such seeds are probably mostly self-pollinated. 

 Also, in choosing seed-trees to be saved in logging operations, the de- 

 sirable practice, judging from present knowledge, would seem to be to 

 leave them in small groups; or if left singly, the seed trees should be 

 left close enough together to insure adequate cross-pollination by the 

 wind. 



It is well recognized that hybrids between species often will not 

 come true when reproduced by seed. Consequently the Institute has 

 given some attention to the possibility of reproducing pines by bud- 

 ding and grafting, which are the usual commercial methods of propa- 

 gating practically all orchard fruits and many ornamentals, in order 

 to insure trueness to type. Though these methods of reproducing 

 pines are still in the experimental stage, the preliminary tests of 



