120 APPLICATION OF PRINCIPLES. 



prevention of stagnant water collecting about the 

 roots ; and the injury committed by worms, upon the 

 roots of plants in pots, is chiefly produced by these 

 creatures reducing the earth to a plastic state, and 

 dragging it among the potsherds so as to stop up the 

 passage between them, and destroy the drainage.* 



One of the means of guarding the earth against an 

 access on -the one hand, and a loss on the other, of too 

 much water, is by paving the ground with tiles or 

 stones ; and the advantages of this method have been 

 much insisted upon. But it is certain that, in cold 

 summers at least, such a pavement prevents the soil 

 from acquiring the necessary amount of bottom heat ; 

 and it is probable that,,what with this effect, and the 

 obstruction of a free communication between the at- 

 mosphere and the roots of a plant, the practice is disad- 

 vantageous rather than the reverse, f 



* [Glazed flower-pots are totally unfit for most plants, except 

 with the most careful attention to drainage, and even then they are 

 much inferior to common unglazed ones. The latter permit the 

 excess of water to escape through their porous sides, which is impos- 

 sible in the glazed pot ; in which, if the aperture at the bottom 

 become stopped, the earth is sodden with water, the plant suffers 

 and soon perishes. A. J. D.] 



f Here, again, it is necessary for the American reader to make 

 allowances for the differences of climate. Covering the soil in 

 summer, is, in this country, one of the most valuable aids to good 

 cultivation ever put in practice. The best mode of doing this is, 

 indeed, not by paving, but by what is technically called mulching. 

 This consists in spreading over the surface of the ground, so far as 

 the roots of tree or plant extend beneath i^ a layer of tan-bark, 

 saw-dust, barn-yard litter, straw, salt-hay, sea-weed, or the like, of 

 sufficient thickness to maintain, as nearly as possible, an uniform 



