200 F. B. GUTHRIE AND R. HELMS. 



arsenic in the soil, the injurious effect increasing as the 

 proportion of arsenic becomes greater ; with *1 per cent, 

 arsenic the plant does not come to maturity. The presence 

 of '01 per cent, arsenic is without injurious effect upon the 

 growth of the plant. 



The following table summarizes the results obtained : — 



Effect upon germination and subsequent growth of the wheat plant 

 of different percentages of injurious substances in the soil. 



Germination Germination 

 affected. prevented. 



Growth affected. 



Growth 

 prevented. 



NaOl '05 *20 



*05 to '15 (recov.) 



•20 



Na 2 C0 3 # 30 *5 to 1/0 



> '10 



•40 



NH 4 ONS *005 -01 



•001 



•005 



Na01O 3 above *01 *05 



•001 



•003 



As.j0 3 *05 above 0*5 



•05 



•10 



Attention must be drawn to the fact that in these experi- 

 ments the injurious substances were incorporated with the 

 soil prior to planting, and that there was no accumulation 

 of them in any one place. In actual practice the fertilisers 

 which are liable to contain these deleterious ingredients 

 are applied in such a way that they are concentrated in the 

 first few inches of the surface soil. This is especially the 

 case when the fertiliser is drilled in with the seed, in which 

 case they are concentrated in the immediate neighbourhood 

 of the germinating seed. For example, *2 per cent, sodium 

 chloride in the soil was found in the above experiments to 

 be absolutely fatal to the growth of wheat. This amount 

 represents about 5,000 fbs. or nearly 2\ tons of salt distri- 

 buted over an acre of soil of average weight to a depth of 

 six inches. Such a dressing would not be applied in practice, 

 but the same injury would result to the plant if the few 

 pounds of soil in its immediate neighbourhood and from 

 which it draws its food-supply were charged with salt to 

 the same extent. 



