Drainage. 679 



inferior hay. The rot in sheep and some of the diseases in cattle are 

 clearly traceable to the effects of wet pastures. 



6. The low temperatures of the plants in summer, caused by the 

 increased evaporation from their surface of the superfluous water 

 taken up with their organic food, and the consequent slowness of all 

 essential chemical changes in the body of the plant. 



7. Disease in timber, and more particularly in the larch, and the 

 lodgment of corn crops — more particularly wheat — from their becom- 

 ing what is called root-fallen before harvest. In many cases rotten- 

 ness of heartwood and stag-headedness in timber are seen to be the 

 results of excessive moisture in the soil. 



Among the many beneficial results of drainage may be mentioned — 



1. The increased friability, and therefore more easy and complete 

 pulverization of the soil, which not only renders every particle of 

 nourishment contained in it available for root-food, but also admits 

 air, without which vegetation languishes. In thoroughly drained 

 and well-worked soils the interspaces amount to one-fourth of the 

 whole bulk, so that when cultivation extends to a depth of eight 

 inches there will be in every acre of ground 12| millions of cubic 

 inches of space available for the supply and circulation of air, and 

 every extra inch of depth broken up calls into activity upon the same 

 area about 235 tons of fresh soil. 



2. Deep drainage, by the removal of the water from the subsoil, 

 causes the descent of that in the upper stratum, which sucks the air 

 down after it ; thus every fall of rain dislodges and afterwards causes 

 the renewal of the air. 



3. Eain brings down from the atmosphere ammonia, nitric acid, 

 carbonic acid, and saline particles, which enrich the soil. Electricity 

 generates the two former in the air, and the lower layers of a fall of 

 sncw are particularly rich in ammonia. When rain-water flows off 

 the surface of land, it not only carries these substances to the nearest 

 brook, but also washes the soluble parts of manure from the soil, 



4. In well-drained land vegetation gets an earlier start in spring, 

 makes more rapid and larger growth, and attains an earlier maturity, 



5. Drainage equalizes the temperature througliout the soil, as the 

 warmth of the air and of the upper soil is carried down to the lower 

 strata. It also promotes healthy growth by enlarging the ranges of 

 temperature from the heat of summer to the cold of winter. In very 

 wet land the temperature rises so little in summer that the range 

 throughout the year is seldom more than 10'^, unless during a season 

 of drought a soil becomes baked, and cracks or opens. Upon 

 moderately dry soils, on the contrary, the range is often as much as 

 35° ; and Humboldt tells us that between the tropics the heat of the 

 soil often rises above 124?. 



