1924] Collins: Inlieriiance in Crepis capillaris (L.) WaUr. 275 



GENERAL DISCUSSION 



In order to establish and preserve true breeding strains of the 

 different types observed in the cultures, type plants were self- 

 pollinated in successive generations. This most intense type of 

 inbreeding affected these cultures in very much the same way as 

 inbreeding has affected maize. Reduction in size and a slower rate 

 of gT0\Ai;h were the most noticeable results of inbreeding together 

 with a slight increase in sterility. Most of the experiments to show 

 the effect of inbreeding in plants have been with domesticated forms 

 in which it is possible to have a genotypic constitution that might not 

 exist in a wild state, because characteristics which would unfit the 

 individual for survival in natural conditions are often preserved 

 under the artificial conditions of cultivation. The inference is that 

 wild species would differ in fewer genes than their cultivated relatives. 

 However, the inbreeding experiments on Drosophila (Castle, 1906) 

 produced no bad effects. Collins (1919) states that self-fertilization 

 in teosinte, a wild relative of maize, causes no loss of vigor such 

 as is known to occur in maize. On the other hand, Darwin (1876) 

 concluded that wild species which are naturally cross-pollinated are, 

 on the whole, adversely affected by inbreeding. It appears then that 

 the results of inbreeding any race, cultivated or wild, would be an 

 index to its genotypic heterozygosity or homozygosity. With this as 

 a criterion, there is indicated a condition of germinal heterozygosity 

 in Crepis capillaris. There appears to be a certain similarity between 

 wild heterozygous species of Crepis and the cultivated races of maize 

 in the type of recessive genes which persist in the genotype. In maize, 

 a number of genes are present which produce characters that are so 

 abnormal (sterility, extreme dwarfs, albinos) that they are propa- 

 gated only with difficulty and would seldom be found under natural 

 conditions. Examples of similar forms have appeared in inbred 

 strains of Crepis. It may therefore be considered that natural selec- 

 tion has not eliminated these genes from the germinal material of the 

 wild species. The genes in Crepis which affect vigor also produce 

 results comparable to similarly acting genes in maize. 



Evidence of the genotj'pic heterozygosity of capillaris has also 

 been gained from another source. Seeds have been obtained from 

 Avidely separated localities and grown side bj^ side in the greenhouse 



