DESCRIPTION OF PLATE VIII. 



Melon wilt. The result of soil inoculations. Hothouse experiment. Washing- 

 ton, D. C. Photographed April 17, 1895. Soil inoculated in 1894 with internal melon 

 fungus brought from South Carolina. 



1. Two healthy and 3 diseased plants; S. One healthy and 3 diseased plants. 



In this stage of growth the first symptom is a drooping of the cotyledons ; this is 

 followed by flaccidity of the plumule and a bowing over of the hypocotyl. The parts 

 above ground and the roots also are sound externally— i. e. they are not wounded, 

 rotted, softened, shriveled, or browned in any way. In this early stage of the dis- 

 ease there is little or no fungus in the hypocotyl, but the vessels of the taproot are 

 plugged. ' After photographing, water was withheld from these plants, and as they 

 were iu a dry room they soon died, the healthy ones included. On April 24 each of 

 the 6 plants which were wilted when photographed bore the conidia beds of the 

 external Fusarium, and a further examination showed the bundles and parenchy- 

 matic tissues of these plants to be full of the internal mycelium and microconidia. 

 On the contrary, the 3 plants which were healthy when photographed contained no 

 internal fungus, and there were no Fusarium beds on the surface, although the 

 plants were under a bell jar in moist air for a day or two prior to the examination. 



' June 29, 1894, about 1,500 hills of watermelons were planted by the writer on a 

 sandy field in South Carolina, which had been infected from stable manure, and on 

 which most of the melon vines had been destroyed by this fungus in May and June of 

 that year. The disease began soon after the plants came up, and in 6 weeks nearly all of 

 the young melons had wilted, altogether perhaps eight or ten thousand plants. The 

 cotyledons first became flabby and drooped, the first true leaf then wilted, the hypo- 

 cotyl lost turgor and bowed over to the ground, and the plants finally shriveled — i. e., 

 the symptoms were precisely the same as those subsequently obtaiued in Washington 

 with pure cultures of the melon fungus. A hundred or more of these wilting plants 

 were examined microscopically, and in each one the fungus was found in the vessels 

 of the hypocotyl or taproot or both in quantity sufficient to account for the disease 

 and commonly nothing else was present. In many plants which were not pulled 

 until the second or third day of the wilt, the fungus was found pushing out into the 

 parenchyma cells and fruiting therein, as shown on PI. II, 5. July 14 the writer 

 removed 14 healthy-looking young melon plants from as many difierent hills in this 

 field and examined them microscopically for the presence of the fungus. Vines had 

 recently wilted in each of tliese hills. The big seedlings were growing rapidly 

 and appeared to be perfectly healthy above ground and below. In 12 of these 

 plants no fungus could be found. In 1 there was an abundance of the fungus in 

 the big central duct of the taproot and in some of the smaller vessels, but none 

 could be found in the hypocotyl. In the other, there was also no fungus in the hypo- 

 cotyl save doubtfully a thread or two in one vessel, but there was plenty of it in the 

 big ducts of the taproot about 1 centimeter below the crown. No hyph?e threads 

 were observed in the i^areuchyma cells of the roots, which were white and appeai-ed 

 to be entirely sound. These two plants would have wilted in a day or two, and the 

 history of the experiment shows that the other 12 would subsequently have contracted 

 the disease. 

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