TO RETAIN MOISTURE. DRAINAGE. 41 



do something ; and fertilizing with substances which 

 attract moisture, will do still more. 



Every thing done to improve the soil makes it retentive 

 of moisture. Clay, mixed with a sandy soil, converts it 

 into a retentive loam. The*, remains of vegetable and 

 animal substances form a spongy matter in the soil, 

 which acts as a reservoir to retain the moisture and other 

 food of plants, and yield it only to their roots. 



125. The rain, as it falls, always contains carbonic 

 acid, ammonia, and other elements of plant nourishment. 

 If it sink into the earth, the soil absorbs all these precious 

 materials, and allows the superfluous water to escape 

 only after having left its contribution in the soil. Besides, 

 if the rain be allowed to run off from the surface, it 

 forms streams and little torrents, and carries with it 

 much of the loose and most valuable portions of the soil. 



The soil should therefore be kept, for some depth below 

 the surface, so mellow and penetrable, that the rain, 

 instead of running off, shall sink into the ground. In 

 ploughing a side hill, the furrows must run horizontally 

 along the slope, so that each furrow may detain the water 

 as it falls, and prevent its forming gullies, which it will 

 do, if the furrows run up and down the hill. 



126. Excess of wet is also sometimes to be feared, 

 especially when the water has no way of running off, but 

 remains stagnant, either beneath or above the surface, for 

 it then causes the plants with which it comes in contact 

 to mould and decay. We must then have recourse to 

 ditching and drainage. 



127. Drainage is an operation by which we draw off 

 the superabundant water from the soil and from the earth 

 lying beneath the soil, where it would not otherwise 

 escape. It is eilected by placing lines of porous earthen 



