2 FIELD CROP PBOhUCTION 



latter class are to be found many of the plants that injure 

 and produce disease in the cultivated forms. To this 

 group belong the rusts and smuts that attack the grains, 

 the blights and wilts that lay low the vegetables, and many 

 other injurious, as well as some useful forms. 



In their usefulness to man, plants vary greatly. They 

 are of service to him principally in furnishing food, cloth- 

 ing, and shelter. They are also a factor in many industries, 

 the products of which supply in some form or other the 

 needs of man. Every industry, in fact, no matter how far 

 removed from the growing of plants it may seem to be, is 

 either directly or indirectly dependent upon it. The 

 fundamental basis of anj' industry is to be found in the 

 food supply of the people who engage in it, and of the 

 people who consume the commodities produced. Men 

 derive their supply of food principally from two sources, 

 plants and animals. The animals, however, are either 

 directly or indirectly dependent upon plants, so that, in 

 the last analysis, the food supply of the nations of the 

 world and consequently the existence of all the industries 

 of the world are dependent upon the production of plants. 

 Not all plants, however, are useful to man, many of the 

 most troublesome diseases that attack the crops being 

 plant gro's\i:hs. 



1. Classification of plants. — Because the plant king- 

 dom is made up of these multitudes of widely differing 

 forms, it has been necessary for botanists, for purposes of 

 study, to classify them into various groups. This branch 

 of the study is called systematic botany, and has occupied 

 the attention of botanists for many years. The classifica- 

 tion has to do with the arranging of plants into groups, 

 based upon their similarity of parts, — their evident 

 relationship. While it is not necessary for the general 



