Control Measures 221 



tubers is necessary if one wishes to avoid these troubles. 

 Provisions for ventilation should be made when the tubers 

 are placed in storage. A potato tuber contains living 

 protoplasm which gives off carbon dioxide, water and 

 a certain amount of heat, and when provision is not made 

 for ventilation, black-heart or center decay may occur. 



Disease-resistant varieties 



These various control measures have been discussed 

 because it is necessary to adopt some or all of them if one 

 is to grow healthy tubers. However, each practice adds 

 to the cost of producing the crop. If such measures do 

 not increase the yield or add to the value of the tubers, 

 they are not worth putting into practice. If it were pos- 

 sible to obtain potatoes that would not become diseased 

 even when subjected to the parasite under favorable con- 

 ditions for infection, much labor and expense would be 

 saved. It is well known that certain individual plants as 

 well as animals have shown marked resistance to diseases 

 that ordinarily occur on their kind. By selection and 

 breeding, it has been possible to obtain highly resistant 

 plants producing crops of good quality. Notable ex- 

 amples are wilt-resistant melons, cotton and flax, rust- 

 resistant wheat and anthracnose-resistant beans. For 

 several years scientists have been endeavoring to secure 

 a satisfactory strain or variety of potatoes that is blight 

 resistant. Some varieties have been secured that have 

 shown a fair degree of resistance to blight or rot. Unfor- 

 tunately, a variety that seems to show a slight degree of 

 resistance to blight may show considerable susceptibility 

 to rot, and varieties showing resistance to early blight 

 may be subject to late blight. William Stuart of the 



