1912.] Sterilisation of Soil for Glasshouse Work. 8 1 5 



ment, however, requires to be repeated with a larger number 

 of plants. 



Cucumbers. — The gross-feeding cucumber benefited more 

 from partial sterilisation, the plants fruiting better on the 

 steamed soil. A similar result has been obtained in another 

 house, where also the earlier ripening on the steamed soil 

 was very noticeable. 



Secondary Effects of Partial Sterilisation. 



The secondary effects of partial sterilisation arise from two 

 causes^: (1) the plant does not live on its usual nitrates but 

 on ammonia, at any rate until reinfection of nitrifying 

 organisms has taken place; other soluble compounds may be 

 utilised also ; (2) some of the soil decomposition products 

 have a physiological action on the plant, modifying it in 

 certain ways. 



Retardation of Germination and Seedling Growth. — The 

 grower's first experience of partial sterilisation may be very 

 disappointing; he will often find that seed germinates more 

 slowly and produces smaller seedlings in the treated, and 

 especially the steamed soils, than in the untreated soils. 

 The precise cause of the retardation is not yet ascertained, 

 and consequently no remedy can be suggested, but it prob- 

 ably arises from the excess of ammonia and other decom- 

 position products, which are useful enough for older plants, 

 but form too aldermanic a diet for the seedling. The amount 

 of retardation varies with the soil, the method of sterilisation, 

 the seed, and the conditions of growth. It was very slight, 

 if it occurred at all, on the chalky loam used for the spinach 

 and radish experiments. It was very marked in a rich 

 cucumber soil, and still more on a turf, and was more pro- 

 nounced the higher the soil had been heated, up to a certain 

 point. There are indications, however, that the harmful 

 effects passed off after a time. Often there was^ no retarda- 

 tion, but an acceleration both of germination and of seedling 

 growth in soil heated only to 130 0 F. 



Poor seeds and old seeds appear to be most affected. 

 Tomatoes appear to be specially susceptible, more so 

 perhaps than cucumbers. Different varieties are not 

 equally susceptible. In working with melons, for ex- 



