252 BREEDING CROP PLANTS 



kohl-rabi. The parental forms did not appear in the F 2 genera- 

 tion. Drumhead cabbage crossed with Thousand-headed kale 

 produced 204 plants in F 2 . Of these, 176 resembled a dwarf 

 type of Thousand-headed kale with leaves broader than usual 

 and fewer branches; 26 resembled cabbage; and two plants 

 were much like brussels sprouts. 



The difficulty of a study of inheritance in the Brassica genus 

 arises from the heterozygous condition of many forms and the 

 self-sterile condition. Before the results are accepted as ex- 

 amples of non Mendelian behavior, a criticial study in which all 

 facts are considered should be made. In cabbage there is appar- 

 ently a complicated inheritance. The above results are satis- 

 factorily explained on a multiple-factor hypothesis. In crossing 

 heterozygous forms, the FI generation may be as variable as the 

 F 2 . In the inheritance of any particular character, the number of 

 factor differences may be so large as to make the appearance of 

 parental forms improbable in a small F z generation. 



Breeding. The breeding of cabbage resistant to yellows (Fusa- 

 rium conglutinansWollenw.) at the Wisconsin Experiment Station 

 (Jones and Oilman, 1915) is of great economic importance. 

 Less than a decade ago, truck farmers in certain sections of Wis- 

 consin were so discouraged from the ravages of yellows that they 

 were about to abandon cabbage growing. The method of pro- 

 ducing resistant cabbage strains may be briefly summarized. 

 It had been noticed that there were usually a few plants which 

 escaped the disease in a field where nearly all plants were badly 

 infected with the organism. These apparently resistant plants 

 were selected on the basis of type. After storing over winter, 

 all that were of the same general type were planted together 

 and were far enough removed from any other similar planting 

 to insure against contamination by foreign pollen. Selfed 

 seed was not obtained but most plants not bagged set seed 

 abundantly. Some plants were eliminated because of low seed 

 production. Progeny of the retained plants were grown sepa- 

 rately and their resistance to yellows was tested. In this way 

 several strains of cabbage highly resistant to yellows have been 

 produced. Further studies have been reported and numerous 

 resistant varieties have been produced (Jones et al, 1920). The 

 writers emphasize the fact that resistance is not absolute and 

 that environmental factors influence very markedly the develop- 

 ment of the disease. They state, however, that: 



