116 



THE SOIL. 



The l-4th saturated turf contained a little above 

 one-half (0*83 gramme) more phosphoric acid than that 

 in the pure turf (1*586 grammes) ; the potash was 

 doubled ; and the amount of nitrogen was increased 

 only by ^ T th. The 'crop, however, exceeded that ob- 

 tained from the plants grown in pure turf, not by ^d 

 (corresponding to the quantity of phosphoric acid 

 added), but it was thirteen times as large. The feeble 

 manuring had caused the turf in the second pot to ren- 

 der thirteen times more nutritive matter for the forma- 

 tion of seed alone, and for the entire plants about thirty 

 times more than the pure turf. 



It is evident that only a small proportion of the ash- 

 constituents in the pure turf were present in a form 

 suitable for the nutrition of the bean-plant. They could 

 not be absorbed, because they were in chemical combi- 

 nation in the substance of the turf. To use a somewhat 

 imperfect figure, the nutritive elements in the pure turf 

 may be imagined to be surrounded by the turfy sub- 

 stance, which hinders their contact with the roots ; 

 while in the saturated 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 were as follows : 



It is not difficult to understand why this should be 

 so. The fact that the J-saturated turf yielded twice as 

 much crop as corresponded to the amount of manure, 

 proves that the absorbent root-surface had come in con- 

 tact with double the number of nutritive turf particles. 



