Some Diseases of Beans. 



289 



drops of water. In this way they reach healthy plants near by. This 

 explains why beans should not be cultivated or handled in the early 

 morning while the dew is still on them or directly after a shower. The 

 spores of the anthracnose fungus are scattered only when they are wet. 

 This will also explain why a warm rainy season is so favorable to the 

 development of the fungus. The spores require moisture in which to 

 be distributed and in wdiich to germinate. A relatively high temperature 

 is also most favorable to the disease. The spores are produced in un- 

 limited numbers in the spots on the pod. Fig. 106 shows the spores 



taken on the point of a pin 

 and placed in a drop of water. 

 Only one of these tiny spores 

 is necessary to start a spot. 

 Under favorable conditions 

 these spores spread from pod 

 to pod until practically every 

 bean in a large field may be 

 affected. Sometimes " string 

 beans " that appear to be per- 

 fectly clean and free from the 

 disease will become very badly 

 spotted if left in boxes or 



/ 



Fig. 106. — Spores of the anthracnose fungus 

 taken on the point of a needle and placed in 

 a drop of water. Magnified about 55 times. 

 The large blur is a mass of the spores from 

 ivhich Others have become detached and scat- 

 tered about in the water. 



bags for a short time. This 

 frequently occurs during ship- 

 ment to market. In such cases 

 the beans are either infected 

 before or during picking or 

 become contaminated from a 

 few spotted pods that have 

 been overlooked and put into the bags wdth the clean beans. No spots 

 2i'i!l appear on the leaves, stems or pods unless spores find their ica\ to 

 these parts of the plant. The spores may be scattered by the cultivator, 

 the pickers, by animals, or by the wdnd in damp or rainy w^eather. 



The disease in the seed. — ;\s the threads or mycelium of the fungus 

 penetrate deeper into the pod they finally reach the seed within (Fig. 105). 

 In the unripe condition the seed-coat is easily penetrated by the mycelium 

 and the fungus is thus established directly in the seed itself. Unless the 

 seed is entirely destroyed by the fungus, it ripens and the enclosed my- 

 celium becomes dormant. The presence of the fungus in the seed may 



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