BREEDING OF VEGETABLES 249 



1. Those which are normally cross-pollinated but which set 

 seed freely on selfing and show no evidence of sterility. 



2. Those which are wholly or partially self-sterile. 



3. Those which are cross-fertilized owing to the dioecious 

 condition. 



Much more study of the mode of pollination of vegetables is 

 necessary before it is possible accurately to classify vegetables 

 according to their mode of reproduction. The crops here 

 considered have been purposely chosen as illustrations of breeding 

 results within these three groups. 



RADISH 



Origin, Inheritance, and Breeding. The cultivated radish, 

 Raphanus sativus, was grown by the ancient Greeks and Romans. 

 There has been considerable discussion as to its origin. Some 

 writers have thought that the cultivated form with its fleshy 

 root arose directly from R. raphanistrum. This belief was ap- 

 parently substantiated by experiments in which the wild form 

 was grown under cultivation and after several years cultivated 

 radishes were obtained. Riolle (1914) tested this hypothesis by 

 a controlled experiment. The wild form was grown under culti- 

 vation and self-fertilized. Three years of selection failed to 

 produce roots which resembled the fleshy roots of R. sativus. 

 On the other hand, when the wild and cultivated forms were both 

 grown on the same plot and seed was saved from the wild form, 

 it was found to be an easy matter, after three years' selection, to 

 obtain roots which resembled the fleshy roots of R. sativus. 

 These results were believed to be due to natural crossing of the 

 wild and cultivated forms. This hypothesis was tested by 

 making an artificial cross. Segregation for root condition oc- 

 curred in FZ. This led Riolle to conclude that former experiments 

 in which cultivated radishes were obtained from the wild 

 through selection were best explained through natural crossing. 



R. sativus roots contain sugar while wild roots contain ho 

 sugar. FI crosses contain less sugar than the cultivated forms. 

 The presence of starch in the root of the wild radish, particularly 

 in the bark, is a character which separates it from the cultivated 

 varieties. This proved a dominant in crosses. Cultivated 

 radishes show various color intensities. Color is apparently 

 inherited in much the same manner as in other crops. Individual 



