12 TRUCK-FARMING AT THE SOUTH. 



in wet seasons. The total absence of water would be de- 

 structive to vegetation, for it is itself necessary to plant 

 life; but undrained land is not merely wet, it becomes 

 water-logged, and through absence of air, the plants are 

 drowned out. When, however, water passes through, and 

 away from the laud, air takes its place, and also passes 

 through the drains, and finds its way into the overlying 

 soil, increasing its fertility and pulverizing it. The rea- 

 son why drained land gains heat, and the temperature of 

 water-logged land decreases, is the lack of heat-conducting 

 power in water, or the fact that air can not be transmitted 

 downwards through water. When land is saturated with 

 water, the heat is expended in evaporating the moisture, 

 instead of warming the land, and during this evapora- 

 tion the temperature is reduced. Undrained land be- 

 comes sour in wet weather, and the formation of sub- 

 stances injurious to vegetation is encouraged. The ab- 

 sorbing power of soil is so great that ammonia and other 

 fertilizing agents of water and air are arrested in their 

 passage through it, thus enriching the soil; while the 

 water on undrained land washes over the surface, carry- 

 ing off into the water courses the fertility that might be 

 saved. In undrained land, the passage of moisture, en- 

 couraged by evaporation from the surface, is upwards, 

 whereas in drained land, the current is downwards 

 to the level of the drains, supplying the roots with 

 aerated moisture in condition to be taken up by them. 

 An excess of water in the soil produces such a saturated 

 state of the atmosphere, as to prevent a healthy perspira- 

 tory action of the leaves of plants growing upon it, and 

 growth is retarded. 



PREPARING THE SOIL. 



Efficient drainage being provided, the land should be 

 broken up and pulverized as deeply as possible. A mass 



