VI.] DRAINAGE 115 



hurdles or temporary reed fences across their land. 

 Similarly, stones upon the surface of the land both help 

 the ground to warm up more quickly and maintain the 

 stock of water later in the season when droughts 

 set in. 



The effects of drainage upon cultivated land afford 

 several illustrations of the principles underlying the 

 operations of cultivation. In the first place, the drained 

 land is warmer and therefore earlier, because as the 

 level of permanent water is no longer near the surface, 

 less water will be brought up to be evaporated ; conse- 

 quently, drying and warming of the surface soil can take 

 place comparatively quickly. At the same time the 

 temperature of the air above the soil is also found to be 

 raised by drainage. In the second place, with the 

 lowering of the water-level in the soil, air is introduced 

 to greater depths, the root system of the crops can 

 extend farther, and in consequence the plant has a 

 greater soil layer to draw upon, and is thereby better 

 able to resist a drought. Lastly, the introduction of air 

 more deeply with the soil and the replacement of the 

 old stagnant water conditions by a steady movement of 

 water through the soil, results in the improvement of its 

 texture ; the clay particles are flocculated both by the 

 occasional dryings and by the salts that are washed 

 through ; to a certain extent also the very finest particles 

 of all are washed down into the drains. The improve- 

 ment of the texture of the soil by drainage is of course 

 a question of time, and only becomes apparent some 

 years after the drains have been put in. 



Just as the drainage of a heavy or a waterlogged soil, 

 by reducing the amount of water with which it is 

 burdened, causes the soil to warm up more quickly in 

 the spring, and therefore to become earlier, so the 

 question of early or late soils is largely determined by 



