REASONS FOR DRAINING. 261 



well in a wet soil, but not one in ten of those cultivated by 

 the farmer. The following table shows the proportion of 

 useless and useful plants on different soils. Whole number 

 of plants are, in 



5. An excess of water injures and destroys the fibrous por- 

 tions of the roots, or spongelets, by means of which nourish- 

 ment is received. This effect takes place always when the 

 water becomes stagnant and putrescent, as it is liable to be- 

 come, when the land is level and the sub-soil retentive. In 

 some cases the tissue is decomposed, and the joints of the 

 stem separated. In others, the plant rots ofT at the ground, 

 especially if there is little light and heat. 



6. An excess of water excludes the influence of heat and 

 air, two indispensable agents to the growth of plants. De 

 Condolle regards the influence of stagnant water about the 

 neck of plants, as operating simply to exclude the oxygen of 

 the air ; but Lindley more properly attributes the injury to 

 the low temperature of the soil, in which water is suffered to 

 accumulate. 



7. Experience shows that however well a soil may be con- 

 stituted in its mineral ingredients, and however rich it may 

 be in humus or geine and salts, no cultivated crop will flour- 

 ish well unless the surface of the soil, and the soil itself is 

 made dry during the growth of the crop, and when required 

 to be worked by the plough or the hoe. 



"It is because of the danger," says Lindley, "of allowing 

 any accumulation of water about the roots of plants, that 

 drainage is so very important. In very bibulous soils this 

 contrivance is unnecessary ; but in all those which are tena- 

 cious, or which, from their low situation, do not permit su- 

 22* 



