336 ELEMENTARY STUDIES IN BOTANY 



A few years ago the cotton fields of the southern states 

 were attacked by a very destructive disease. When the 

 ravaged fields were examined by experts, it was discovered 

 that certain cotton plants were untouched by the disease ; 

 in other words, these individuals were immune to this partic- 

 ular disease. This fact suggested that this immunity might 

 be a character that could be inherited, and so immune indi- 

 viduals were selected for breeding, and it was found that their 

 progeny was also immune. In this way, by pedigree culture, 

 immune races of cotton have been developed. It must not 

 be supposed that an immune race is immune under all condi- 

 tions, but this method enormously increases our success in 

 preventing disease. This same method can be applied to all 

 plants for all diseases, so that it is possible to look forward to 

 the time when we will be cultivating only disease-resistant 

 races of plants. 



41. Drought-resistance. A few years ago the wild orig- 

 inal of our cultivated wheat was discovered in Palestine. 

 This wild wheat grows in dry conditions, in situations that we 

 would call " arid/' such as are found in this country in New 

 Mexico and Arizona. A drought-resistant wheat would be 

 of the first importance, provided it was also of good quality. 

 This combination of drought-resistance and good quality 

 has now been secured through plant-breeding, so that it has 

 become possible to insure wheat crops against drought. 

 More than that, the drought-resistant wheat thus secured 

 is found to be disease-resistant ; that is, to the rust disease. 

 This combination of drought-resistance, disease-resistance, 

 and good quality promises to increase greatly the production 

 of wheat. 



A peculiar race of corn has been found in cultivation in 

 China, which has a structure that makes it drought-resistant. 

 Corn is peculiarly in danger of drought during the period 

 when pollination occurs, and if a " dry spell " occurs at that 

 period the corn crop is seriously damaged. If this drought- 



