35 



obsolete long before this. Instances have occurred where experi- 

 ments have been carried on by the use of similar remedies which 

 have given exactly opposite results. It must be borne in mind that 

 it is impossible to draw reliable deductions from experiments which 

 have been tried only once or twice upon a small scale. Especially is 

 this true in regard to nematodes, as they normally manifest different 

 periods of activity. We have observed instances where nematodes have 

 disappeared from soil where no treatment has been applied and 

 under circumstances which rendered their disappearance not easy of 

 explanation. Upon this point it should be remembered that we do 

 not as yet fully understand all of the environmental conditions which 

 play a role in their life history, and for this reason we are more 

 likely to fall into errors in interpreting results from experiments. 

 Our own experiments which were very extensive have convinced us 

 that the application of chemical substances to the soil is of little 

 practical value in ridding it of nematodes. 



(b). THE DESICCATION METHOD. 



It is well known that drying is very destructive to nematodes and 

 we have repeatedly seen the effects of this in our laboratory and 

 greenhouse. Vahne* who has advocated this method of treat- 

 ment takes advantage of a long dry spell of weather, either in 

 the fall or spring, and by working the soil repeatedly with plows 

 and cultivators, thus giving it a chance to become as dry as possible, 

 claims to have succeeded in making it an uncongenial habitat for the 

 worm. After the drying process is partially completed he applies 

 imslacked lime at the rate of 2-4 tons to the acre which assists fur- 

 ther in the desiccation of the soil and destruction of the worm. He 

 has tried this method with reported success upon fields where sugar 

 beets were planted, and he further maintains that it is efhcient as a 

 remedy for certain parasitic fungi such as the damping fungus 

 (Pythiun de Baryanum) Leaf spot of beet, (Phoma Betae) etc. This 

 method is undoubtedly a very cheap one of controlling nematodes pro- 

 vided it works satisfactorily, although it must be difficult out of doors 

 in a variable climate to always find the right season for its applica- 

 tion. We have frequently found that drying small masses of soil in 

 the greenhouse for a number of weeks completely rids the soil of 



*J. Vahne, Zur Frage d. Vetilgung v. Nematoden aus schadlichen Pilzen im Boden, 

 Wiener landw. Ztg. 1897, p. 732. 



