Fakm Drainage. 363 



the necessary conditions exist, viz. : the exchision of light, a 

 certain amount of moisture, heat, and the presence of air. 

 Any material which, without entirely excluding the air, will 

 shade the seed from light, furnish the necessary moisture, 

 and allow the requisite degree of heat, will favor the chem- 

 ical change which we call sprouting In proportion as the heat 

 is reduced by the action of evaporation, and as the air is 

 excluded by water, is the sprouting retarded, and in case of 

 a complete saturation for a certain length of time, which 

 varies in different kinds of grain and plants, decay takes 

 place, as we all know from our own experience. I have in 

 my mind now an instance where a large field of potatoes, 

 planted on a fiat piece of land contiguous to a stream, was 

 immersed by a heavy rain for a short time, three days, if I 

 am correct, and not a hill grew except a few small patches 

 on ground high enough to be above the water, 



I have used the embryo plants to illustrate my ideas, as 

 they more perfectly show the effect than more mature 

 plants ; but although the others may live through, they are 

 materially affected by an unfavorable state of the soil. As 

 all superfluous water must either pass down through the soil 

 or be evaporated, we will consider the effect of evaporation 

 on the soil. 



Water exposed to the air is constantly "drying np," w^hich 

 is changing from a liquid to a vaporous form, in which form 

 it occupies two thousand times more space than when in its 

 liquid form, to maintain which it requires a large amount of 

 heat, which is taken from the ground and air, which are 

 thereby made correspondingly cooler. The practical work- 

 ing of this can readily be seen by reference to the change 



