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time the roots of the mustard become well covered with galls, which 

 is an indication that the worms are confined within the tissues of the 

 host, and before they have laid their eggs, the roots of the mustard 

 are plowed up and are either exposed to the drying rays of the sun 

 or are raked up and burned. In this way the catch-crop method not 

 only destroys a great many nematodes contained in the infested 

 soil, but also hundreds of eggs, which if left would in a 

 short time give rise to innumerable adult worms. Dr. N. A. Cobb 

 (\. c. p. 170.) states that the female nematodes lay from 300-400 eggs, 

 and when we consider that some galls are one inch or more in diam- 

 eter and contain numerous females the crop of young must be enor- 

 mous. We have frequently obtained hundreds of them when only 

 two or three females were introduced. By continual planting catch 

 crops in the soil the nematodes can be reduced to a considerable 

 extent, as the experiments of Kiihn and Hollrung seem to show, 

 but it is impossible to completely rid the soil of the worms. 

 Such a method might be of some value in our Southern States where 

 the nematodes are very abundant and attack a large variety of cul- 

 tivated plants, but in the north, where the Heterodera cannot stand 

 our winter climate and where they attack almost entirely green- 

 house plants, more effective remedies must be sought. 



The Effect of Chemicals upon Nematodes. 



Our first experiments relating to the control of nematodes were 

 largely along the line of many of those we have just described, that 

 is to say we endeavored to find some chemical method of control. 

 The problem confronting us was to be sure somewhat difiierent from 

 that confronting those having large areas of infested soil out of 

 doors with which to deal. Granting that the chemical method of 

 treatment might be more or less successful out of doors, we 

 ought nevertheless to require some more absolute method in green- 

 houses, because there is much less area of soil there to be treated 

 and it is under conditions which can be more readily controlled. Never- 

 theless we made many hundreds of experiments with chemicals in 

 order to give them a thorough trial and to see if such a method of 

 treatment was practical. We carried on our experiments simultane-- 

 ously in the laboratory and in the greenhouse which were connected 

 with each other. Parts of the greenhouse had been devoted to nem-- 

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