532 INSECTS AFFECTING VEGETATION 



chum lindemuthianum, which lives as a parasite in the tissues of 

 the bean. This fungus is a plant, as much a plant as the bean on 

 which it lives. It has a thread-like mycelium that grows into the 

 tissue of the bean to obtain food for its growth and development and 

 it produces spores that serve the purpose of seeds by which it spreads 

 to healthy beans and so reproduces itself. In fighting the anthrac- 

 nose fungus, we are fighting a parasitic weed, in its habits not great- 

 ly unlike the dodder which often destroys alfalfa. 



The disease makes its first appearance on the bean seedlings, 

 as they come up. It may then be detected, on at least some of the 

 young plants, as brown discolored sunken spots or cankers on the 

 seed-leaves or the stem. This early appearance of the disease is due 

 to the fact that the fungus is usually carried over winter in the seed 

 and so is already in the bean when it is planted. In severe cases the 

 spots or cankers may be so numerous as to cause heavy loss in the 

 seedlings and result in a poor stand. Sometimes the stem is so badly 

 diseased or eaten near the base that it falls over and dies. Usually 

 so few of the seedlings are attacked that the presence of the disease 

 in a field is at first overlooked. Nevertheless, as the season advances 

 the fungus spreads to healthy plants near by, by means of its multi- 

 tude of tiny spores produced in these spots on the seedling and before 

 the grower knows it his entire field may be badly affected. 



From the spots on stem and seed-leaves of the seedlings the 

 spores find their way to the large leaves and branches of the rapidly 

 growing plants. The large veins of the leaf are frequently eaten 

 through and killed by the fungus, and holes or cracks with black- 

 ened margins appear in the blade. While this may not entirely kill 

 the leaf, it greatly lessens its efficiency as a starch maker and so in- 

 directly but effectively reduces the yield of seed. Many times, how- 

 ever, the attack is so severe that the leaf stems are cut off and the entire 

 plant is practically ruined. 



It is from the attack of the disease on the pods that the most 

 direct and apparent damage to the crop results. During the time of 

 blossoming and previous, the fungus has been spreading and becom- 

 ing established on the stems and leaves, and it now attacks the young 

 and succulent pods. With their tender growing tissue full of water 

 and food materials, these pods offer the best conditions for the 

 growth and development of the parasite. Spores from the spots on 

 the leaves and stems fall on the pods where, in the presence of 

 moisture and the high summer temperature, they germinate, form- 

 ing a little sprout or germ tube, which penetrates the tender skin of 

 the pod and, 'branching in the juicy tissues, gives rise to an an- 

 thracnose canker. These first appear as little brown or rusty spots 

 which enlarge and darken until nearly or quite black. The dead 

 tissue dries and settles, causing a little pit or sunken place in the pod. 

 In the center of the spot the spores of the fungus are now produced 

 in great abundance. They ooze out and pile up, forming little pink 

 masses easily seen with the naked eye. These masses of spores are 

 held together by a kind of glue or mucilage which, when dry, sticks 

 them tightly to the spot. When a drop of rain or dew falls on the 



