AND COLLEGE, PUSA 3 FOR 1915-1C 87 



•oxidation consequent on the cultivation, had failed to reach. 

 Parallel plots with barley illustrated this effect more mark- 

 edly than those with wheat, no doubt owing to the later 

 formation of the secondary root system in the former crop 

 and its consequent dependence for a longer period of its 

 early growth upon the original deeper roots. Laboratory 

 work on nitrification and on the growth of seedlings in 

 water and soil cultures demonstrated the possibility of 

 separating substances from certain bacterial cultures, from 

 decomposing organic matter and from anaerobically incu- 

 bated soil, whose toxicity to nitrifiers, and in greater con- 

 centration to seedling plants was demonstrable under these 

 •conditions. 



Interesting observations were made as to the interfer- 

 ence with the growth of seedlings resulting from the bac- 

 terial invasion of the unexhausted and still attached seed 

 and the consequent absorption by the plant of toxic bacte- 

 rial by-products. This invasion occurred most readily in 

 water-logged soil and more especially in the presence of 

 bacteria derived from anaerobically incubated soils of high 

 organic matter content. Copper sulphate was found to 

 neutralize most of the toxic bodies obtained in this way, and 

 seeds treated with this salt were found to be immunized to 

 some extent, although not entirely or invariably, against 

 this action. It is suggested that some such treatment might 

 be advantageous when sowing in wet soils, although the re- 

 sults of field trials have so far not yielded conclusive 

 results, owing to the difficulties associated with its use and 

 the unfavourable effect upon germination which copper 

 sulphate has been found to exert in many instances. 



Amongst soil toxins produced by bacterial action 

 nitrites are well known to exert a prejudicial effect upon 

 plant growth ; it has been found that their presence in soils 

 is not alone due to the reduction of nitrates already formed, 

 although this is of frequent occurrence, but that in many 

 of the soils examined in this laboratory nitrites accumulate 

 to some extent before nitrate formation becomes evident, 

 even under conditions apparently favourable to nitrification. 



