472 



STATE BOARD OF 'AGRICULTURE. 



ness, the diffusion becomes smaller. Thoiigh this does not change the 

 coellicieut of dilfusion, i. e. the amount of comjiounds diffusing per 

 unit, it decreases the number of units and consequently the amount of 

 food diffusing towards the cells and the amount of metabolic jtroducts 

 diffusing from the cells. The result is an insufficient food supjilv com- 

 bined with the accumulation of harmful products. The most abundant 

 oxygen supply could not increase the rate of development under these 

 conditions. The greatest development will take place when oxygen 

 and food diffuse to the cell at least as fast as they are used up; the 

 demand for both increases with the growth of the cells because the 

 active mass increases. 



(O 



O 



n ^? ... ^^ 



Fig. 1. 



This does not mean, however, that decomposition in the drier soils 

 must remain incomplete. As long as the moisture film is sufficiently 

 coherent to allow diffusion from one soil particle to the other, the de- 

 composition will be complete, only a long time will be required to do 

 this. The endpoiiit of bacterial decom})osition will be the later, the 

 thinner the moisture film. The data of Table VI show quite con- 

 clusively that the decomix)sition in the moister soils is faster in the 

 beginning, but soon comes to a stop, while the drier soils work slowly 

 and steadily, and finally are ahead of the moister samples. The oxygen 

 in the moist samples is soon exhausted and is replaced very slowly if 

 at all. In the drier soils, the diffusion of food to the cells is slow, but 

 constant, and the oxygen supply is sufficient to decomi>ose all available 

 food. The Series III and IV especially show this very ])lainly. In 

 both series, there are two soils, each with and without fertilizer, at 



