3 



ciai effects depend upon many different causes, some 

 chemical, some mechanical. 



Water is absolutely essential to vegetation; and 

 when land has been covered by water in the winter, 

 or in the beginning of spring, the moisture that has 

 penetrated deep into the soil, and even the subsoil^ 

 becomes a source of nourishment to the roots of the 

 plant in the summer, and prevents those bad effects 

 that often happen in lands in their natural state, from 

 a long continuance of dry weather, 



When the water used in irrigation has flowed 

 over a calcareous country, it is generally found im- 

 pregnated with carbonate of lime; and in this state it 

 tends, in many instances, to ameliorate the soil. 



Common river water also generally contains a 

 certain portion of organizable matter, which is much 

 greater afier rains, than at other times; and which ex- 

 ists in the largest quantity when the stream rises in a 

 cultivated country. 



Even in cases when the water used for flooding 

 is pure, and free from animal or vegetable substances, 

 .it acts by causing the more equable diffusion of nutri- 

 tive matter existing in the land; and in Very cold sea* 

 sons it preserves the tender roots and leaves of the 

 grass from being affected by frost. 



Water is of greater specific gravity at 42 Fah- 

 renheit, than at 32, the freezing point; and hence in 

 a meadow irrigated in winter, the water immediately 

 in contact with the grass is rarely below 4O, a degree 

 of temperature not at all prejudicial to the living or- 

 gans of plants. 



