820 Sterilisation of Soil for Glasshouse Work, [jan., 



siderable damage in certain districts, and informs us that 

 steam sterilisation and treatment with a certain disinfectant 

 effectively kills the spores and leaves the soil capable of 

 carrying perfectly clean healthy plants. An outbreak of 

 "gumming" (Cladosporium scabies) occurred on the 

 cucumbers in a house where some of our experimental plants 

 were growing, but there was no obvious difference in the 

 incidence of the disease between the treated and the untreated 

 sections of the borders. 



Weed seeds are all killed at 200 0 F., so that boxes or pots 

 of steamed soil are readily distinguished from untreated soil 

 by their freedom from weeds. 



The Treatment of Glasshouse "Sick" Soils. 



Our investigations show that "sickness" of tomato, 

 cucumber, and other soils is due to two causes acting together 

 — a lowered efficiency of the plant food-makers, and an 

 accumulation of disease organisms. Both these causes are 

 removed by partial sterilisation, most completely by heating 

 to 200 0 F. which has the further advantage of effecting 

 some decomposition of the organic matter, but also to a 

 greater or less extent by various antiseptics. We have care- 

 fully studied eight "sick" soils, and found in every case that 

 partial sterilisation effected a satisfactory improvement. The 

 chemical and other examinations that have been made need 

 not be referred to here ; it is sufficient to give the weight of 

 the plants to show that the fertility of the soil has been 

 restored, and the weight of the fruits to show that the new 

 growth is not simply rank foliage but leads to greater fruit 

 production. (See table on next page.) Fig. 6 shows two of 

 the plants, and Fig. 7 shows the relative yield of fruit. 



The present method of dealing with "sick" soils is to 

 throw them out from the glasshouse and replace them by 

 virgin soils, carted sometimes from a considerable distance. 

 "Sickness" so speedily sets up in a cucumber house, with its 

 high soil and air temperatures (8o° F. or more), and its 

 extraordinarily high manure and water supply, that the soil 

 has to be thrown out each year at considerable expense, and 

 at the sacrifice of all the valuable manurial residues. Soil in 

 a tomato house, which is run at an altogether lower pitch, lasts 



