47 



when injured in sonic particular way. If these plants are infected 

 chiefly during the seedling stage, then the growth of young plants in 

 uninfected seed beds and their transplantation to infected soils only 

 when they have passed out of the receptive stage would atl'ord relief. 

 This is offered, however, only as a working hypotliesis. All we yet 

 know is that frerpiently many plants of cotton and cowpea on infected 

 land come to a healthy maturity, i. e., there is not such a sweeping 

 general infection as in case of the watermelon. Possibly, however, 

 this is a statement depending on an insufticient number of observa- 

 tions. It is true so far as my observations have extended.^ 



Melon plants grown for several weeks in good earth, i. e., plants with 

 one true leaf and the second one beginning to develop, are still freely 

 subject to soil infection. The shortest period of incubation observed 

 by the writer has been about C days, i. e., the cotyledons wilted, as 

 shown in PI. VIII, the first or second day after the plants emerged 

 from the ground. The longest period of incubation, or rather lapse of 

 time between infection of the soil and appearance of the disease, was 

 81 days. In this case the seed was planted and the soil of the pot 

 infected April 25 and the vine showed no symptoms of disease until 

 July 15, when it suddenly wilted. Thirty-one other vines of the same 

 series contracted the disease between June 1 and July 11. The soil of 

 these pots was reinfected May 20, no cases having appeared. In both 

 instances the fungus used was derived from a big, arcuate, several- 

 septate, external conidium. Vine 32, which wilted at the end of 81 

 days, was 4 feet long. There was an abundance of fungus in the ves- 

 sels and it bore only the small, colorless, elliptical microconidia; these 

 were non-septate, straight or slightly curved, and measured G.5 to 24 

 by 2 to 4 //. In field culture a period of 80 days frequently intervenes 

 between planting and the first appearance of disease in a given vine. 



The question of parasitism of the cotton fungus was left an open one 

 by Professor Atkinson, as shown by the following citations: 



"The Fusarium was considered not to be a sufficiently aggressive 

 parasite to be able to make its way into the ducts of the circulatory 

 system unaided." It is suggested that a dampiug-oflf fungus may first 

 open the way. The only two infections obtained by him with the cot- 

 ton Fusarium were on plants with open wounds made by the "sore- 

 shin" fungus. "The discoloration and disease of the ducts is started 



I Mr. Orton obserred in 1899 in various parts of Soutli Carolina what had previ- 

 ously escaped my attention, viz, that every cotton plant in the vicinity of dead 

 and dying plants is dwarfed and does not bear as much fruit as it should, even 

 when it shows no symptoms of the disease. This dwarfing is most conspicuous 

 toward the end of the growing season and is associated with the presence of the 

 fungus in the vascular system of the side roots of the plant, the vessels of the tap- 

 root and of the stem being free or very nearly free from the fungus. This may 

 help to explain the statement often made by cotton growers that one stalk in a hill 

 will blight and another will not. In reality, it may be only a question of degree, all 

 being more or less affected. 



