112 BIOLOGY OF PLANTS. 



ing and tilling his soil that its moisture, carbonic acid, oxy- 

 gen and other constituents, may circulate freely through it, 

 to all parts of the roots. By giving to the soil a proper con- 

 sistency, and by supplying it with vegetable and mineral sub- 

 stances, the elements of the atmosphere are made to act upon 

 the vital functions with greater power. Thus, by giving to 

 the soil greater absorbing power, it will feel the influence of 

 the dews ; by draining it, the injurious effects of water will 

 be prevented, and the action of the air facilitated. If, there- 

 fore, the farmer cannot cause the rains and dews to descend at 

 his will, he can so prepare the soil that the highest advantage 

 may result from the influence of these agents. 



2. The influence of heat. How can this agent be applied 

 by the farmer ? Simply by adding to the soil, mineral or vege- 

 table substances, which will give it the power of absorbing 

 and retaining the heat of the sun, or which will, by their com- 

 binations, produce heat in the soil. By the fermentation of ma- 

 nures, great quantities of heat are given out ; hence, if the 

 soil is naturally cold, manures should be applied before they 

 are fermented, and incorporated with the soil that the heat 

 may be equally distributed. By increasing the fertility of the 

 soil, its power of retaining heat will be increased. 



3. Electricity. How is the influence of this agent con- 

 trolled by the farmer ? If a soil is acid, that is, in a state of 

 negative electricity, it is wholly barren ; if a soil is alkaline, 

 that is, in a positive state of electricity, it is also barren ; but 

 when its acids are neutralized by its alkalies, then it is in a 

 state favorable to fertility, and the more completely the elec- 

 tro-powers of the soil are balanced, the more fertile will the 

 soil become. Now, by analysis, the electrical state of the soil 

 can be determined, and the substance applied which will re- 

 store the equilibrium of the electric forces. From the analy- 

 sis of soils of different degrees of fertility, it is surprising to 

 notice how narrow the limits are, between absolute barren- 

 ness and a high state of fertility. One soil, for example, 



