WATERING THE SOIL. 171 



great necessity of attending to the due humidity of the soil, and 

 to the prevention of stagnant water collecting about the roots. 

 In like manner the injury committed by worms upon the roots 

 of plants in pots chiefly consists in these creatures reducing 

 the earth to a plastic state, and dragging it among the pot;- 

 sherd.s so as to stop up the passages between them and destroy 

 the drainage. 



One of tiie means of guarding the earth against an access on 

 the one hand, and a loss on the other, of too much water, is by 

 paying the surface of ground with tiles or stones, ind the 

 advantages of this method have been much insisted upon. But, 

 iu cold summers at least, such a pavement may prevent the 

 soU from acquiring the necessary amount of heat ; and it may 

 in some degree obstruct the free communication between the 

 atmosphere and the roots. It is therefore a. practice that 

 should be adopted cautiously. 



It is in places fuUy exposed to the sun, and liable to "bum" 

 in summer, in consequence of loss of moisture, tbat paving 

 answers best. On heavy land where trenches have been formed to 

 hold peat for American and similar fibrous-rooted plants, it is sometimes 

 found impossible to keep them alive in summer until the surface ip 

 paved, after which they succeed perfectly. Here, however, it is found 

 that the best kind of paving consists of round pebbles of gravel spread 

 over the surface, with peat sifted between them. Flagstones, tiles, or 

 large nodules of flint are objectionable. 



More commonly recourse is had to the operation of simple 

 watering, for the purpose of maintaining the earth at a due 

 state of humidity, and to render plants more vigorous than they 

 otherwise would be ; an indispensable operation in hot-houses, 

 but of less moment in the open air. It is, indeed, doubtful 

 whether, in the latter case, it is not often more productive of 

 disadvantage than of real service to plants. When plants are 

 watered naturally, the whole air is saturated with humidity at 

 the same time as the soU is penetrated by the rain ; and in this 

 case the aqueous particles mingled with the earth are very 

 gradually introduced into the circulating system, for the 

 moisture of the air prevents a rapid perspiration. Not so 

 when plants in the open air are artificially watered. This 



