108 DISEASES OF TROPICAL PLANTS CH . 



It was first attributed by Atkinson to Fusarium 

 vasinfectum, but E. F. Smith afterwards found what he 

 believed to be the perfect stage of the fungus, and 

 described it under the name of Necosmospora vasinfecta. 1 

 It evidently enters roots through wounds. It penetrates 

 to the fibro-vascular bundles of the plant where it grows 

 rapidly, producing an abundant mycelium and spreads 

 into the stem. In a short time it plugs the ducts of 

 the bundles, and interferes with the transmission of 

 water from the roots to the upper parts of the plant. 

 The effect of this cutting off of the supply of water is 

 the same as a prolonged drought, and the leaves usually 

 wilt, dry, and fall. In most cases the wilting takes 

 place very rapidly, but in some cases the leaves dry 

 very slowly and then fall. Occasionally only a part of 

 the plant dies. 



In some cases the disease causes a dwarfed growth 

 but does not kill the plant. However, it can be readily 

 detected by splitting the stem which, if affected, will 

 show a dark discoloration of the normally white internal 

 tissues. 



The disease is subject to great variations. It 

 usually starts with a yellowing of the edges, or between 

 the larger ribs of the lower leaves. These discoloured 

 parts may become white but later turn brown, die, and 

 fall. This condition spreads over the entire plant, 

 sometimes slowly and sometimes rapidly. 



The fungus produces an abundance of spores both 

 in the soil and upon the old dead leaves. These spores 

 will retain their vitality in the soil for very long periods 

 of time, and may be carried to other localities in a great 

 many different ways. 



This is one of the most widely distributed diseases of 

 the cotton. It is very common throughout the cotton- 

 growing districts of the United States, and has been 



1 The organism causing the wilt of the cow-pea and the water-melon are so 

 similar to the organism which causes the wilt of the cotton that it is 

 impossible to distinguish them. Although these organisms are so much alike 

 they will not transmit the disease from one crop to another. The okra is also 

 attacked by a fungus which causes a similar disease. 



