IRRIGATION AND DRAINING. 81 



waters that have flowed out of the sewers of cities, or past 

 slaughter-houses and certain manufactories, and received the 

 rich contributions of vegetable food thereby afforded, are the 

 most beneficial. Meadows thus irrigated, in the neighbor- 

 hood of Edinburgh, have rented by the acre, at the large 

 sum of $250 per annum ; a price predicated not only on the 

 enormous amount of grass yielded, but on the high prices at 

 which it was retailed in that city. But when none of these 

 can be procured, pure spring water, apparently destitute of 

 any soluble matters, may be advantageously used. 



Additional effects of Irrigation. Besides its drainage of 

 fertile matters from % remote distances, which are deposited 

 on the fields overflown, water freely absorbs the gases, (car- 

 bonic acid, oxygen and nitrogen, &c.,) in proportions alto- 

 gether different from those existing in the air, and brings 

 them to the roots, by which they are greedily appropriated ; 

 and in its onward, agitated progress over the field, it again 

 absorbs them from the air, again to be given up when de- 

 manded by the roots. When the water is permitted to 

 remain stagnant on the surface, this good effect ceases ; and 

 so far from its promoting the growth of the useful and cul- 

 tivated grasses, they speedily perish, and a race of sour 

 and worthless aquatic plants spring up to supply their 

 place. 



Another and important office that water fulfils in minis- 

 tering to the growth of vegetation, is in disposing the soil 

 to those changes, which are essential to its greatest fertility. 

 Gypsum requires 460, and lime 778 times its bulk of water 

 at 60 Far. to dissolve them. Others among the mineral 

 constituents of plants, also require the presence of large 

 quantities of water, to fit them for acting on the soil, and to 

 adapt them for vegetable assimilation. 



TIME FOR APPLYING- WATER TO MEADOWS. 



In those regions where the winters are not severe, water 

 may be kept on the fields during the entire season of frosts. 

 This prevents their access to the ground, and on the ap- 

 proach of warm weather, the grasses at once start into life, 

 and yield an early and abundant growth. But in general, 

 this system cannot be successfully practiced. The water 

 may be admitted at proper intervals, freely during the spring 

 and early part of the summer, when vegetation is either 

 just commencing or going forward rapidly. It is sufficient 

 to flood the surface thoroughly, and then shut off the water 

 4* 



