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saprophytes, that grow upon it, which is a good indication that the 

 organic matter contained in the soil has undergone changes through 

 the action of the heat. We have ourselves observed more than once 

 certain species of saprophytic fungi growing upon our steamed beds 

 which have never shown any tendency to grow on unheated soil, 

 although with the exception of being steamed the soil was exactly the 

 same as that upon which they never appeared. 



Effects of Heating the Soil Upon Other Greenhouse Pests. 



Besides the destruction of nematode worms, and the gaining of 

 robust and vigorous plants which steaming the soil gives rise to, 

 there are other beneficial effects worthy of being taken into consid- 

 eration. Many of the fungous and insect pests to which our green- 

 house plants are subject find their normal habitat in the soil. In 

 our experiments upon heating the soil in the beds we killed thou- 

 sands of red spiders, and we presume that we did the same with the 

 cucvnnber aphis, or with the eggs, as we were remarkably free from 

 them, although the soil had previously been used for cucumber crops 

 which were badly contaminated with aphis. This latter statement, 

 however, in regard to killing the aphis, is nothing more than a con- 

 jecture, as Entomologists tell us that they do not know where the 

 aphis breeds, but they surmise that it breeds upon particles of organic 

 matter in the soil or upon the old cucumber vines thrown out upon 

 the compost heap. The soil undoubtedly harbors many of the 

 spores of the mildews which are common to cucumbers, tomatoes 

 and lettuce. 



One of the most common and troublesome diseases to young 

 cucumbers is the so-called " damping fungus," Pythium De Barya- 

 num, which attacks the young plants at the surface of the ground and 

 causes them to wilt and collapse. We have repeatedly found as a 

 result of heating that this did not make its appearance when they 

 were subjected to a temperature which was over 140° or 150° F.; 

 when, however, the temperature went below these points the fungus 

 appeared to be accelerated in its growth and development and 

 damping was more likely to show itself than in normal pots. This 

 fungus must be distinguished from the ordinary " damping fungus " 

 (Botrytis) which attacks begonia cuttings, etc., in the propagating 

 pit. Sterilizing the soil for this fungus would be of no account as 

 the spores (conidia) of this species are everywhere and only await a 



