276 



General Botany 



Wheat, barley, oats, and rye have all had their areas of culti- 

 vation extended by the discovery of, or production of, new- 

 varieties with qualities which enabled them to be grown in other 

 climatic regions. 



Greater resistance to diseases. A striking example of breeding 

 for resistance to a plant disease is the successful production of 

 watermelons resistant to " wilt." All the edible varieties were 

 highly susceptible to this disease. By crossing the Eden variety 

 of watermelon with an inedible citron which was highly resistant, 

 hybrids of great vigor and productiveness were produced. After 

 8 years of selection and trial a uniform edible variety was isolated 

 which possessed the good qualities of the Eden watermelon and 

 the wilt resistance of the citron. Curiously enough, this resist- 

 ance is maintained throughout the eastern United States, but 

 in Cahfornia the new melon is susceptible. This emphasizes the 

 importance of breeding plants for particular regions. 



\gric . Expt. Sta. 



Fig. 174. In a field of cabbage that was almost entirely destroyed by yellows, a plant that 

 had formed a good head was found. This plant was slaved for seed. 



