M ancJiester Memoirs, Vol. Iviii. (19 14), No. 0. 9 



manured plots. Another set of the soil solutions was 

 boiled before use, since boiling had been reputed to 

 destroy the toxin and would, at any rate, kill off any 

 bacteria that might be factors in the result. Lastly, in 

 another set the solutions were evaporated, the residue 

 ignited and dissolved afresh in a minimum quantity of 

 hydrochloric acid, then diluted to the original volume. 



In this series boiling was without effect, whether the 

 solutions contained added nutrients or not ; the residue 

 left on evaporation, after ignition and revolution, gave 

 generally lower results, in some cases to a marked degree. 

 The soil solutions from completely manured plots gave 

 higher yields than the artificial solutions of corresponding 

 strength. 



In order to ascertain whether the results were limited 

 in any way by the nature of the plant (it might be ob- 

 jected as regards Series I. that barley and wheat are so 

 closely akin as to excrete the same toxin), the experiments 

 in Series II. were repeated with sunflowers, white lupins, 

 and buckwheat. These plants are far from being so suitable 

 for experiment as barley, and the results were somewhat 

 erratic, but they in no way indicated the presence of a toxin 

 in the soil solution which depresses the growth of barley, 

 but ex hypoihesi'xs without effect on plants of another order. 

 Finally, in Series III., both barley and peas grew freely in 

 the soil solutions from the completely manured plots and 

 in the solutions from the incompletely manured plots 

 after repair of the deficiency by adding salts as in the 

 artificial solutions made up with pure salts. Indeed, the 

 superiority, though hardly large enough to be significant, 

 lay with the plants grown in the soil solutions. Thus the 

 experiments yielded no evidence of the existence in soils 

 on which a particular plant had been growing for sixty 

 years and upwards of a soluble " toxin " having a 

 depressing effect upon the growth of that plant. 



