774 EXPERIMENT STATION RECORD. 



by crossing. . . . By crossing different species we can form more variations and 

 mutations in half a dozen generations than will be developed by ordinary variation 

 in a hundred or even a thousand generations. . . . 



" The evolution of species is largely dependent on (Tossing the variations contained 

 within it. Forms too closely bred soon run out, because generally only by crossing 

 docs variation appear. It is of great advantage to have the parents a certain distance 

 apart in their hereditary tendencies. If too close together, there is not range enough 

 of variety. If too far apart, the developed forms are unfitted for existence, because 

 too unstable. Correlated changes work together to produce the effect of muta- 

 tions. . . . Radical changes of environment for a series of generations will produce 

 a tendency to sport, but hybridization will bring it about far more abruptly and, for 

 practical plant or animal breeding or for scientific study of all these variations, far 

 more satisfactorily." 



Mr. Burbank has produced a number of species by hybridization which he believes 

 to be as good as nature itself has produced. It is asserted that there is a close anal- 

 ogy between hybridization and grafting. An instance is cited in which Promts myro- 

 balana var. pissardi was imported from France and grafted on the Kelsey plum, n 

 variety of Prunus triflora. The graft did not bloom, but its presence on the tree 

 brought about a cross between the two species. Many hundred descendants of this 

 cross are now living. 



In one sense hybridization is believed to he only a mode of grafting. A diagram 

 is given showing the zone of life and parallelism of results in crossing and grafting. 

 Mendel's law which holds good for the tribe of peas has not been found to be gener- 

 ally true so far as Mr. Burbank's experiments go. 



The results of crossing are sometimes very simple, and at other times are so com- 

 plicated that to follow them requires the highest skill, and even then may be utterly 

 impossible. 



An instance is cited in which a Siberian Rubus (A', cratsegifolius) was crossed with 

 a California blackberry (R. vitifolius). Some of the hybrids obtained combine the 

 best qualities of both fruits, and out of over 5,000 second generation seedling every 

 one has proved true to seed. A hybrid red poppy was obtained by uniting the 

 opium poppy with the oriental poppy. The second generation hybrids thus obtained 

 all prove perennials, and blossom every day in the year, while the parents are annu- 

 als and blossom only for a few weeks. The hybrid poppy produces no seed. New 

 spineless cacti for stock-feeding purposes have been secured by crossing together 5 

 species of Opuntia. 



It is stated that crosses are sometimes more vigorous than their parent, and at 

 other times the reverse is true. A peach-almond cross is cited, in which the hybrid 

 produced a tree ten times as large as either parent of the same age. 



Heredity, L. Burbank (Amer. Florht, 24 {1905), No. S7~ J , pp. 149, 150).— A. paper 

 presented at the meeting of the American Breeders' Association, held at Champaign, 

 111., February 1-3. 



Heredity is defined as "the sum of all the effects of all the environments of all 

 past generations on the responsive ever-moving life forces." Crossing is stated as 

 the grand principal cause of all the species and varieties of earth, sea, and air. Rel- 

 ative to the formation of acquired characters, the author states that "similar envi- 

 ronments produce similar results on the life forces, even with the most distantly 

 related plants or animals. This fact alone should be proof enough, if proof were still 

 needed, that acquired characters are transmitted." 



The parallelism of grafting and hybridizing is pointed out. "Grafting or budding 

 may be called a bio-meehanico-chemieal combination. While crossing by seed is 

 more of a bio-chemical union, yet this last union is often more truly mechanical than 

 chemical as in the case of a mosaic union, which is not unusual when the cross is 

 too abrupt. In fact, every gradation from a purely mechanical union to one of per- 



