8i8 Sterilisation of Soil for Glasshouse Work, [jan., 



and they show certain peculiarities in steamed soil. They 

 are particularly susceptible to the toxic substance present; 

 clover still refuses to grow in pasture soils heated to 208 0 

 in March, 1908, although it is sown three or four times a 

 year. Toluol, however, has much less drastic an effect and 

 will even produce a marked increase in crop if the proper 

 nodule organisms are added. Much depends on the nature 

 of the soil : the chalky loam already referred to produced, 

 even after steaming, no bad effect on dwarf beans and sweet 

 peas although no improvement was seen, whilst it not only 

 caused no injury to sainfoin, but led to an increased crop. 

 Mr. Holmes, of Norwich, also tells us that he has raised 

 sweet peas perfectly well on heated soil. Much further in- 

 formation is wanted about the effect of soil treatment on the 

 growth of leguminous plants. 



Effect of Partial Sterilisation on Insect and other 

 Pests, Weed Seeds, etc. 



Eelworms. — From the growers' point of view the 

 eelworms of the soil may be divided into two groups : 

 the parasitic forms, such as Heterodera radicicola, 

 which causes the knots or club on the roots of tomatoes and 

 cucumbers; and the free-living forms, Rhabditis, Diplo- 

 gaster, &c, which so far as our observations go are without 

 injury to the healthy plant. It is easy to demonstrate the 

 presence of the free living forms in a soil, because they tend 

 to cluster round decaying vegetable or animal matter, &c; 

 thus they may readily be trapped in a piece of meat or of 

 mangold, or in a large seed such as the broad bean, left a 

 few days in the moistened soil. But we know of no certain 

 way of detecting Heterodera except by examination of the 

 roots, or the washings from the roots, of the host plant. 



The conditions of greenhouse culture favour the develop- 

 ment of the parasitic eelworms to an extraordinary extent. 

 Fig. 5 b shows the root of a tomato plant grown on a soil from 

 a tomato house; it is no exaggerated specimen, and demon- 

 strates one cause why tomatoes cannot be grown indefinitely 

 in the same soil. A number of soils have been sent 

 to us from commercial cucumber and tomato houses, so- 

 called "sick " soils, all of which contained quantities of Hetero- 



