DISEASES OF CULTIVATED PLANTS 535 



ping of the same land with beans is not desirable and, fortunately, 

 not commonly practiced. 



It is well known that certain varieties are more susceptible 

 than others to this disease. This is notably true of the common. 

 Wax varieties. So far as the writer has been able to discover, no 

 very extensive information on this point is to be had. Numerous 

 Rust Proof varieties have been placed on the market, but while 

 some of them are more or less resistant probably all will spot under 

 conditions most favorable to the fungus. Dependence, therefore, 

 should not be placed on the resistance ability of any variety. All 

 should be thoroughly sprayed if immunity to the disease is desired. 



Bean Blight. The blight is a bacterial disease. It is caused by 

 a minute parasitic plant (Bacterium phaseoli) in form and habits 

 of life quite unlike the anthracnose fungus. These tiny bacteria 

 have no mycelial threads and no spores. Each little cell is a plant in 

 itself. The bacteria increase in numbers by each one simply divid- 

 ing into two which, when full grown repeat the process. Each one 

 is supplied with a long fine flagellum 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. 

 Like the anthracnose, it attacks all parts of the bean above ground 

 but is most conspicuous on the foliage and pods. 



The first evidence of the blight is usually to be observed in the 

 leaves. These show large brown dead patches 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 prob- 

 ably always enter the bean plant through a wound. Judging from 

 some observations made last season, it seems likely that certain in- 

 sects 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 parasite and one that requires further observation before 

 definite statements can be made. Having gained entrance to the 

 leaf, the disease gradually travels down the stem to other leaves 

 and to the pods. Professor Barlow of the Ontario Agricultural Col- 

 lege, has shown that the progress of the disease is comparatively 

 slow. Leaves of beans inoculated with the bacteria did not show 

 symptoms of the disease until the third week. The bacteria increase 

 in such numbers that finally they may fill up the sap tubes in the 

 stem, cutting off the water supply and so cause the entire plant to wilt 

 and die. 



Through wounds or by way of the stem the bacteria find their 

 way into the pods which, if young, may shrivel and die. In the 

 larger pods they produce spreading watery spots which finally be- 

 come more or less discolored but never sunken and black as in the 

 case of the anthracnose. 



From the pod the disease readily gains entrance to the grow- 

 ing seeds. The pods are not destroyed unless attacked when very 

 young, and when ripe they may show considerable discoloration 

 or none at all. The bacteria, however, having gained entrance into 



