THE POD-SPOT OR AISTTHRAClSrOSE 



131 



stalk (Fig. 56) and kill the plant. In this way a fourth 

 of the seeds planted are sometimes killed off. As the 

 leaves develop they are attacked^ the veins becoming- 

 blackened, and discolored spots appearing. Dots of a 

 light pink color appear on the middle of the spot shortly 

 after it has formed. A microscopic examination will 

 show that these dots consist of spore masses held together 

 by a mucilaginous substance^ which is readily soluble in 

 water. When the enveloping mucilage is dissolved the 

 spores are set free, to be blown or washed about, or car- 

 ried to other plants by insects or other agencies. 



Treatment. — Planting in a light soil, on high, 

 well-drained land, is one of the best preventives of this 

 disease. Experiments in New York have shown that it 

 is well worth while to examine the seed beans carefully 

 before planting and reject all that show signs of the dis- 

 ease. Then the young plants may be sprayed with 

 dilute Bordeaux mixture, to which soap enough has been 

 added to make a slight suds, applying first when the 

 plants are two weeks old, and repeating two or three 

 times at intervals of a week or ten days. Or soak the 

 seed in dilute ammoniacal copper carbonate solution. 

 In the case of string beans, where the pods are to be eaten, 

 the spraying must cease earlier than with those crops 

 where the beans themselves are to be harvested. The 

 immediate removal and destruction of all plants or por- 

 tions of plants which become affected is very desirable, as 

 every plant so left becomes a center of infection. They 

 should be taken away and burned or buried. 



Literature. — The best article concerning this dis- 

 ease accessible to the American student was published 

 by Professor Scribner, in the report of the Department 

 of Agriculture for 1887 (pp. 361-364). It is illustrated 

 by an excellent colored plate. Professor Trelease pub- 

 lished an earlier account in the Cultivator and Country 

 Gentleman (October, 1885). Other articles of especial 



