Some Diseases of Beans. 



295 



II. BEAN BLIGHT 

 The blight is a bacterial disease. It is caused by a minute parasitic 

 plant {Bacterium pliascoli) in form and habits of life quite unlike the 

 anthracnose fungus. These tiny bacteria have no mycelial threads and no 

 spores. Each little 

 cell (Fig. 112) is 

 a plant in itself. The 

 bacteria increase in 

 numbers by each one 

 simply dividing into 

 two which, when full 

 grown, repeat the 

 process. Each one 

 is supplied with a 

 long fine Hagclluiii 

 or tail by which it 

 may wiggle about to 

 some extent in the 

 tissues of the bean. 

 The blight attacks 

 the ordinary field 

 and garden varieties 

 and also the Lima 

 Beans. It was first 

 observed in this 

 State by Professor 

 Beach of the State 

 Experiment Station 

 in 1892. Like the 

 anthracnose, it at- 

 tacks all parts of the 



bean above ground 



Fig. III. — "Blight " on pods of Lima beans. From Nciv 

 Jersey Bulletin No. 151. 

 but is most con- 

 spicuous on the foliage and pods. 



The disease on leaves. — The first evidence of the blight is usually to 

 be observed in the leaves. These show large brown dead patches (Fig. 

 109), often spreading through the entire leaf. When wet, the spot is 

 soft and watery, but when dry, becomes papery and brittle. On a badly 

 blighted patch the leaves become dry and curled, as if scorched. The 

 bacteria probably always enter the bean plant through a wound. Judg- 

 ing from some observations made last season, it seems likely that certain 

 insects are in most cases the agents by which this disease is carried from 

 plant to plant. This is an important point in the life history of the para- 



