62 STAKMAN 



Man is completely dependent on plants for subsistence. Important as 

 animals are, it is almost literally true that all flesh is grass. Important as is 

 modern industry, it cannot produce the basic foods needed for human sub- 

 sistence. Basically, man's existence on earth is dependent on plants, and the 

 degree to which he can develop a biotechnology based on science is an im- 

 portant factor in determining how and how many people can live in the world. 



Agriculture, then, is the most basic of all industries, and in the last analysis 

 agriculture is applied botany. The course of evolution of agriculture is traced 

 by the history of the improvement, the adaptation, the nutrition, and the 

 protection of plants that man utilizes directly or indirectly for foods, feeds, 

 and fibers. As plant foods are converted by animals, various branches of 

 zoology become important also, but animals are essentially transformers 

 rather than primary producers of human food. We still are dependent on the 

 process of photosynthesis, which is carried on only by plants; and the prob- 

 lem is to develop a biotechnology that provides the most efficient kinds of 

 plants and then helps them to function as efficiently as possible. Efficient 

 plants must be well bred and well fed, and they must be protected against 

 the debilitating and devastating diseases that continually menace them. 



There are thousands of kinds of plant diseases that attack the thousands 

 of kinds of wild and cultivated plants of gardens, fields, and forests. They 

 cause spots and blotches, rots and cankers, blights and wilts, rusts and 

 mildews, smuts and sooty molds, galls and witches'-brooms. There are more 

 than three thousand kinds of plant rusts that attack grains and grasses, 

 trees and shrubs, the most beautiful flowers of the gardens, and the ugliest 

 weeds of the fields. And there are more than fifteen hundred kinds of powdery 

 mildews that attack oaks and willows, roses and lilacs, wheat and barley, and 

 hundreds of other kinds of plants. 



Disease is universal among all our cultivated plants and most of our wild 

 ones. Some kinds of disease attack many kinds of plants; others attack only 

 a few. Some diseases cause relatively little damage; others are ruthless 

 killers. Some spread slowly; others can spread with frightening rapidity 

 and cause widespread destruction in a short time; they have the ability to 

 become devastatingly epidemic when weather and other conditions favor 

 their development. 



Most epidemic diseases are caused by viruses, bacteria, or fungi that 

 can multiply with amazing rapidity and that can be quickly disseminated 

 far and wide by insects or by the wind. The rusts of wheat and certain 

 other cereal grains have periodically caused catastrophic epidemics for more 

 than two thousand years, and they still continue their destructive careers 

 despite man's best efforts to control them. They are among the most typically 

 epidemic diseases. 



Three of the more than three thousand kinds of plant rusts are among 

 the oldest-known enemies of wheat. There is evidence from many statements 



