E. J. Russell and H. B. Hutchinson 143 



hydrogen peroxide, seemed to be influenced by partial sterilisation. 

 Heat certainly causes decomposition and increases the food material 

 available. These and other factors are under investigation. 



§ 43. Plant groiuth in paiiially sterilised soils. So far as the plant 

 is concerned the difference between the partially sterilised and the 

 untreated soils may be briefly summed up. In the partially sterilised 

 soil organic matter decomposes more rapidly with the production of 

 a greater amount of ammonia, but no nitrate. Plants make greater 

 growth and contain an increased percentage of nitrogen and of phos- 

 phoric acid. 



In the earlier paper on partial sterilisation the question was raised : 

 In what form do plants take up their nitrogen from partially sterilised 

 soils ? The pot experiments indicate that it cannot be taken up as 

 nitrate, but they are not conclusive by reason of the liability to 

 re-infection. In order to make the evidence quite clear a number 

 of plants were grown in conditions where infection did not take place. 



The soil was filled with all proper precautions into sterilised Woolff's 

 bottles with three necks. Through the centre neck the sterilised seed 

 was dropped and a plug of cotton-wool inserted ; in each of the others 

 was fixed a glass tube, one for the water supply reaching to the bottom 

 of the bottle, the other, for the air supply, just dipped inside and was 

 plugged with cotton-wool. The soil was weighed, and the nitrate was 

 determined ; the quantity of nitrate present in each bottle was therefore 

 known. The plants were kept in a special glass house kept as free as 

 possible from dust. 



Water was added at regular intervals so that 18 per cent, should 

 always be present ; the necessary amount was ascertained by weighing 

 the whole apparatus on each occasion. The difficulty of adding water 

 without at the same time introducing bacteria was overcome by 

 permanently connecting a Pasteur flask filled with sterilised water to 

 the Woolff's bottle, and transferring water from the flask to the soil 

 in the ordinary way. When the crop was harvested at the conclusion 

 of the experiment examination was made for the nitrifying organism 

 which, however, was found to be absent. The soils were then again 

 partially sterilised and sown with a second crop ; the results are given 

 in Table 1.5, and photographs of typical plants in Plate VIII, Fig. 3. 



In a second series of experiments nitrifying organisms were added. 



Six bottles formed the unit in each experiment. 



§ 44. It is quite clear that the plants have got their nitrogen from 

 some source other than nitrates. The percentage of nitrogen in the 

 dry matter of the rye is at its lowest (= 2'07 per cent.) in all cases 



Journ. of Agric. Sci. iii 



