ROTATION OF CROPS 179 



■fleeted by it. Corn Buffers from smut, but tobacco 

 docs not. These plant diseases spread much as diseases 

 spread among human bcingl ami animals. Tims per- 

 Bons occupying a room previously occupied by a man 



Buffering with a contagious disease like smallpox or 

 scarlet fever arc liable to contract the disease. The 

 room is said to be infected by the disease, and in a 

 similar way soils become infected by plant diseases. 

 Wheat, for instance, when grown on a soil which the 

 year before produced a crop of wheat affected by ru>t. 

 is liable to contract the disease. But if some other 

 crop is planted which is not liable to this disease there 

 is no danger. A proper rotation of crops, for the rea- 

 ■Ollfl stated, checks the spread of plant diseases. 



168. Examples of Rotation. — The crops used in rota- 

 tion must, of course, he determined by the kind of 

 crops it is desired to <:ro\v. The following examples 

 have been found satisfactory: 



it i«>n 1. ii tobacco, second year wheat, 



third vear wheat, fourth and fifth years clo\ 



Rotation 2, — Krsi year corn, second year oats, third 



wheat, fourth and fifth years clOTST. 

 Rotation 3- ir tobacco, second year wheat, 



third and fourth years ch> 



t ion \. — First year corn, second year wheat, 

 third and fourth years doi 



Rotation 5. — First year cotton, second year wheat, 

 third and fourth years clover. 



In rotations cowpeas or any other suitable legumi- 

 nous crop may be used in place of clover. 



