50 



upon vegetation is, that the soil being stiffened to such 

 an extent the roots of the plants are unable to penetrate 

 it and are thus stifled in their growth, or it is so cold 

 that the roots are discouraged from extending themselves 

 sufficiently to obtain and afford the proper nourishment 

 to the plants. By the evaporation which is constantly 

 going on the heat of the surface is reduced, especially 

 in spring and autumn, thus shortening materially the 

 period of vegetation. It sours the soil, producing a rank, 

 unhealthy vegetation. It occupies the soil to the exclu- 

 sion of air, thus depriving the roots of the most im- 

 portant accessory to vegetation. It excludes the rain 

 water which contains the elements of fertility. It causes 

 surface wasting and the consequent formation of gullies 

 and fissures. It causes the exhalation from the soil of 

 miasmatic odors, which taint the atmosphere and have a 

 deleterious effect upon health. 



On the other hand, the result of thorough drainage 

 will be to cause the pulverization of the soil by remo- 

 ving the source of adhesion, and thus facilitating the 

 mechanical extension of the roots and their consequent 

 development. It elevates the temperature of the soil by 

 allowing the free passage of warm rain water, which at 

 the same time deposits the elements of fertility extracted 

 by it from the atmosphere, thus increasing the resources 

 of vegetation. It increases the power of absorption, 

 which enables the soil to support vegetation in the ab- 

 sence of regular rains. It facilitates the passage of air 

 to the roots, supplying the proper amount of oxygen 

 necessary to them. It deepens the soil, giving the roots 

 of trees a firmer hold, and removing them farther from 



