THE PRESIDENTS ADDRESS. 35 



the characters of dissimilar parents, then grafting often results in 

 hybrids. Those who object to this use of the word hybrid call 

 these combination forms chimeras. 



The subject is too new. and the facts are as yet too perplexing. 

 to give to the situation its biological meaning or its possible 

 practical application. One striking feature, however, may be 

 mentioned as an illustration. In some of these graft hybrids, or 

 chimeras, the tissues of the two parent forms remain entirely 

 distinct, and are related to each other concentrically. For ex- 

 ample, all of the interior of the body of a chimera may be dis- 

 tinctly that of one parent, and all of the peripheral structures 

 that of the other parent. In other words, such a chimera con- 

 sists of one parent ensheathed by the other. The superficial 

 aspect, therefore, is that of the parent form furnishing the mantle ; 

 and since the sexual cells are derived from the cells of the mantle, 

 sexual propagation from such a hybrid results in progeny consist- 

 ing of pure forms, through and through, of the peripheral parent. 

 This carries the recognition of hybrids out of the reach of 

 superficial appearance or even of seedling production. Such a 

 combination would stand the test of constancy applied as final 

 in determining a pure race. It can hardly be doubted that we 

 have been introduced not only to a fertile field for the investiga- 

 tion of problems of heredity, but also to great practical possibili- 

 ties in the manipulation of plants. 



A more recent application of scientific results to practical plant- 

 breeding, and one that has extended its possibihties enormously, 

 is the replacement of mass culture, with its continuous selection, 

 by pedigree culture. This method is directly related to De\"ries' 

 mutation theory, and has been developed most notably by Xilsson 

 of Sweden. Xot only is it really scientific plant breeding, but it in- 

 cludes our fundamental agricultural crops. Xilsson found that his 

 oat and barley crops, grown from pure seed in the market sense, 

 which means seed developed by the old method of mass culture, 

 were very complex mixtures. That is. there was such an amount 

 of variation among the individuals that they seemed to represent 

 many distinct races. Among these individuals, he found repre- 

 sented all the characters he had been tr}-ing to build up by the 

 old method of continuous selection, and many more besides. 

 Accordingly the desirable individuals were selected and pedigree 

 culture was established. The selection of a single individual 

 resulted in a progeny that usually came true. The laborious 



