DISEASES OF CULTIVATED PLANTS 533 



spot the mucilage is at once dissolved, and the spores are set free in 

 the water. At this time any disturbance of the bean plants will 

 scatter these spores in the flying 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 which to germinate. A relatively high temperature is also most 

 favorable to the disease. The spores are produced in unlimited 

 numbers in the spots on the pod. 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 bags for a short time. This frequently occurs 

 during shipment to market. In such cases the beans are either in- 

 fected before or during picking or become contaminated from a few 

 spotted pods that have been overlooked and put into the bags with 

 the clean beans. No spots will appear on the leaves, stems or pods 

 unless spores find their way to these parts of the plant. The spores 

 may be scattered by the cultivator, the pickers, by animals, or by the 

 wind in damp or rainy weather. 



As the threads or mycelium of the fungus penetrate deeper 

 into the pod they finally reach the seed within. In the unripe con- 

 dition 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 myce- 

 lium becomes dormant. The presence of the fungus in the seed 

 may usually be detected by the brown or yellowish discoloration of 

 the seed-coat. When the seeds are badly affected, they become more 

 or less shriveled as well as discolored. It is thus easy to tell with 

 considerable certainty whether seed to be planted is affected with 

 anthracnose. When the seed is planted in the spring the enclosed 

 but dormant fungus is planted with it. The moisture and warmth 

 which stirs the bean to life awakens the fungus also. In the soft 

 and fleshy seed-leaves in which it is imbedded the mycelium finds 

 an abundance of food and grows rapidly, soon forming a spot or 

 canker and producing spores which at once begin again to spread the 

 disease to neighboring healthy plants. (N. Y. [Cornell] E. S. 

 B. 239.) 



Selection of clean seed is of first importance in growing a clean 

 crop. All beans to be planted should be most carefully hand picked 

 and all beans showing discolorations, wrinkles or blisters should be 

 discarded. This cannot be too carefully done. It has been found 

 that in some cases where 95 per cent of the beans were marketable 

 only one per cent was fit for seed. 



As soon as the bean plants are well through the ground, they 

 should be carefully examined and all diseased seedlings pulled up, 

 carried from the field in a sack, and burned. This is the -second step 



