HETEROZYGOTE CHARACTERS. 



55 



pure races, a process which we may call Mendelian analysis, such 

 forms might be of great importance to the breeder. They might 

 render possible the deliberate combination of highly desirable char- 

 acteristics existing in different varieties. Some very interesting 

 work of this kind has been done. Prof. S. M. Tracy, working under 

 the direction of the writer, has thus obtained three races of cassava 

 which reproduce practical^ true to seed. They are now being 

 used in an attempt to propagate this crop from seed instead of from 

 cuttings. If the attempt is successful, and it promises to be so, it 

 will permit a considerable extension of cassava culture into latitudes 

 in which it is not practicable to propagate cassava from cuttings, 

 because of the difficulty of keeping the cuttings over winter. 



In Volume V of the Annual Reports of the American Breeders' 

 Association, Dr. W. T. Macoun, of Canada, reports some very inter- 

 esting facts regarding the seedlings of the Wealthy apple. There 

 was probably some cross-pollination in this case, but the seedlings 

 give very plain evidence of the parentage of this important variety 

 of apple. This is an important and nearly virgin field of investiga- 

 tion, and more work of this kind will be looked for with interest. 



HETEROZYGOTE CHARACTERS. 



In some crosses, or hybrids, characters appear in the first genera- 

 tion of the cross that were not apparent in either parent. These 

 characters may belong to either of two classes. First, they may be 

 due to the heterozj^gote nature of the hybrid. Characters of this 

 class can be taken advantage of by the breeder only when the plant 

 concerned can be propagated vegetatively. In crops propagated 

 from seed a character which is due to the heterozygote nature of the 

 plant which bears it will appear in the next generation in only half 

 the progeny. Such characters can not be fixed by selection; at least 

 no one has as yet succeeded in doing so, and it is highly improbable 

 that it can be done. 



The most common type of such characters is the well-known vege- 

 tative vigor seen in many hybrids. It is not unusual in sorghum 

 fields to see here and there a st,alk which is much larger and taller 

 than the rest of the field. Investigation has shown that these plants 

 are hybrids. The writer has noticed in his work with hybrid wheat 

 that the first-generation hybrid is mu-ch more vigorous and stronger 

 growing than either of the parents as a rule, though this vigor in 

 hybrid wheats is not so marked as it is in sorghum. In corn it is 

 especially marked. Dr. G. H. Shull by the close breeding of two 

 varieties secured practically homozygote strains of them, which 

 were then crossed. The yield of the hybrid was about five times 

 that of the attenuated self-fertilized pure strains. It should be 



165 



