PLANT BREEDING 



361 



while to produce a new form that will be a little earlier than 

 any existing variety. 



Another quality of great importance is the plant's ability 

 to resist diseases. Much attention is being paid by plant 

 breeders to the development of disease-resistant varieties — 



Fig. 203. — Breeding for disease resistance. Seeds were obtained from 

 a single plant which remained healthy in a field of cabbages otherwise 

 badly affected by a disease known as "yellows." The seeds were planted 

 with those of other varieties in a diseased field, and the result is here shown. 

 Only the plants in the row grown from the selected seed were normal. After 

 Jones and Gilman. 



varieties, that is, that are not attacked or are attacked only 

 to a small extent by a particular disease. For some time it 

 has been known that certain apple varieties are little affected 

 by rust ; durum wheat also resists rust ; and varieties of 

 cotton, watermelon, and flax have been obtained that are 

 resistant to a class of very destructive diseases known as 

 wilts. Other characteristics of plants that may be influenced 



