140 DEPARTMENT OF AGRICULTURE GEORGIA. [426] 



and fertilizing gases so well as a natural fall of rain. The 

 necessity for an abundant supply of water in the soil is 

 shown by the fact that water is the exclusive vehicle of the 

 mineral food of plants, and that, without a certain degree 

 of dilution of the solution of plant food in the soil, the latter 

 becomes positively injurious. This is plainly shown in the 

 effects of concentrated commercial fertilizers on shallow soils 

 in times of drouth. Again, water is an essential agent, both 

 in the decomposition of vegetable matter in the soil, and 

 of the disintegration and chemical transformation of min 

 eral suhstances, which, though abundant, would, without 

 this agency, be entirely beyond the reach of vegetation. 



Frost acts an important part in the preparation of min- 

 eral food for plants by the pulverization of rocks, and thus ex- 

 posing their contents to the action of chemical agents. 

 This action of frost is due to the expansion of the water 

 which insinuates itself into the pores of solid substances, 

 freezes, and bursts them asunder. This action exerts a 

 beneficial influence also upon the mechanical condition of 

 compact soils. 



Evaporation, in our climate, is excessive and injurious in 

 its effects, both upon the soil and vegetation upon the 

 soil, by lowering its temperature and forming a crust upon 

 the surface, which prevents access to air; upon vegetation, 

 by the too rapid withdrawal of watery vapor from the 

 leaves of plants, causing the wilting and twisting of the 

 leaves observed during periods of drouth or excessive 

 heat. 



Underdrainage, and deep and thorough pulverization of 

 the soil, are the only practicable preventives of excessive 

 evaporation. 



Where practicable, mulching is the most effectual pre- 

 ventive of injurious evaporation, but it is only practicable 

 on a small scale. 



Warmth in conjunction with moisture, oxygen gas and 



