318 



PLOUGHING AND SUBSOILINO. 



tern of drainage by the ordinary method, than would otherwise have been 

 required.* 



I do not enter into any further details in regard to the application of 

 these principles to the practice of draining, being satisfied that when you 

 have once mastered the principles themselves, the applications will 

 readily suggest themselves to your own minds when circumstances re- 

 quire it. 



§ 4. Of ploughing and suhsoiling. 



I. jrloughing. — Apart from the obvious effect of ploughing the land, 

 in destroying weeds and insects, the immediate advantage sought for 

 by the farmer is the reduction of his soil to a state of minute division. 

 In this state it is not only more pervious to the roots of his corn, but it 

 also gives a more ready admission to the air and to water. 



Of the good effects produced by the easy descent and escape of water 

 from the surface, I have already spoken (p. 306), but the permeability 

 of tlie soil to air is no less useful in developing its natural powers of pro- 

 duction. How important the presence of the air is both to the mainten- 

 ance of animal and to the support of vegetable life, we have had fre- 

 quent occasion to observe. By its oxygen the breathing of animals is 

 sustained, and by its carbonic acid the living plant is fed. On the earthy 

 particles, of which the soil consists also, the influence of these gaseous 

 substances, though not so visible and striking, is of almost equal conse- 

 quence in the economy of nature. Among other immediate benefits 

 derived from the free access of air into the soil, we may enumerate the 

 following : — 



1°. The presence of oxygen in the soil is necessary to the healthy 

 germination of all seeds (page 132), and it is chiefly because they are 

 placed beyond its reach, that those of many plants remain buried for 

 years without signs of life, though they freely sprout when again brought 

 to the surface and exposed to the air. We have also seen reason "to be- 

 lieve (page 77), that the roots of living plants require a supply of 

 oxygen in order that they may be maintained in a healthy condition. 

 Such a supply can only be obtained where the soil is sufficiently open 

 to perrrfft'the free circulation of the air among its pores. 



• It sometimes happens that in sinking an old well deeper 

 for the purpose of obtaining a better supply of water, the 

 original springs disappear altogether. This is owing to the 

 occurrerice at this greater depth, of an absorbent bed, in 

 which the water disappears. By descending still farther, a 

 second supply of water may often be found, but which will 

 naturally ascend uo further than the absorbent bed, by which 

 the whole supply will be drunk np, if not prevented by the 

 insertion of a nietal pipe. Advantage is sometimes taken of 

 the known existence of such absorbent strata, not only for the 

 purposes of draining, but also for removing "vaste water of 

 various kinds. An interestine example ofsucrj application is 

 to be seen at St. Denis, in thePlace aux Gueldres, where the 

 water from the bed /at the depth of 200 feet ascends through 

 the inner tube a— from another bed c, at 160 feet, through the 

 tube b — while between it and the outermost tube, through the 

 space c, it is sent down again after it has been employed in 

 washing the square, and disappears in the absorbent stra- 

 iumd 



— f-^Tpl 



a 



e c 



^ Vl ^ 



e ~ e 



•y— 



