RELATION OF CROr TO FOOD IN SOIL. 



Ill 



able for the nutrition of tlie bean-plant. They could not 

 be absorbed, because they were in chemical combination 

 in the substance of the turf. To use a somewhat imper- 

 fect figure, the nutritive elements ui the pure turf may be 

 imagined to be surrounded by the turfy substance, wliich 

 hinders their contact with the roots ; while in tlie satu- 

 rated turf these elements form the outer coating of the 

 turfy substance. 



The crops of seeds show further that they were not in 

 proportion to the nutritive substances contained in the 

 soil, but that the poorer mixture yielded far more seeds 

 than it should have done in proportion to the production 

 of the richer mixtures. The proportions in the several 

 mixtures w^ere as follows : — 



It is not difficult to understand why this should be so. 

 The fact that the ^-saturated tm-f yielded twice as much 

 crop as corresponded to the amount of manure, proves 

 that the absorbent root-surface had come in contact with 

 double the number of nutritive turf particles. According 

 to weight, the ^-saturated turf contained, in every cubic 

 centimetre, only ^th of the nutritive substances found in 

 the completely saturated turf ; but, by mixing 1 volume 

 of saturated with 3 volumes of unsaturated turf, the 

 former had become far more distributed, and its volume 

 or efficient surface had been made larger. Supposing it 

 were possible to coat 3 volumes of ordinary turf-powder 

 with 1 volume of saturated, so as completely to surround 

 every fragment of the former with saturated turf particles, 

 the bean-plants would, in a soil so prepared, grow as 



