422 TRANSACTIONS OF THE 



plants. Of that otlier part which passes down by filtration to 

 appear again in springs most of it is also evaporated from the 

 land those springs irrigate, but a very small percentage finding 

 its way to the ocean. 



It has been frequently remarked in clearing away the forests 

 of this country and superseding them by a growth of the grasses 

 that the springs become smaller and in some cases dry quite away 

 at times, where previously they had been permanent, and also 

 that the annual freshets in the streams do not rise so high as when 

 the country they drain was wooded. To account for this we may 

 refer to some late experiments in Europe that show that when soil 

 is trenched to the depth of three feet there is no filtration, and 

 that at less depths the plants growing in it can use more water 

 during the season in addition to the rain than what drains away. 

 Indeed common observation shows us that most plants growing 

 on the banks of streams where they obtain an unlimited supply 

 of water by upward filtration are greatly increased in growth. 

 Hence we may conclude that if in addition to culture so deep as 

 to retain all the rain that falls we were to supply some additional 

 water it would increase the growth. 



We are not to conclude from these facts that an unlimited sup- 

 ply of water to a soil is all that is necessary to render it fertile; 

 although a soil in this condition does give a much better growth 

 than one in the opposite state of aridity. Water and air are both 

 necessary for the decay of orgtinlc matter, and consequently for 

 the supply of carbonic acid in the soil on which vegetative growth 

 depends. It is probably by furnishing air as much as by removing 

 water that underdraining produces its effects. It is a well known 

 practical fact, that in those under drains that are working effect- 

 ively, a current of air is continually generated, and this draft is 

 probably connected with the oxidation of organic matter in the 

 soil. 



If the processes of agriculture then, laborious as they are, derive 

 their principal value from the fact that they furnish a steadily 

 continuous supply of water to plants ; and if the fertility of a 

 country may be judged of by its rain gauge; and if we have sun- 

 shine enough to use up all of our rain, and even more if it fell, 

 then we ought to make such arrangements as would save the 

 greatest possible amount of the water that annually falls, and 

 leave as little of it as possible to run away into tl>e sea. In ths 

 case of meadows, when we cannot plow them annually, and whea 

 consequently the soil becomes very hard, so that they are the first 

 to suifer from drought, every little rill should be scrupulously 



