OF THE MOISTURE OF THE SOIL. 115 



earth. As soon as young leaves sprout forth, perspi- 

 ration commences (TO), and a powerful absortion 

 must take place by the roots ; the younger the leaves 

 are, the more rapid their perspiratory action ; their 

 whole epidermis must, at that time, be highly sensi- 

 ble to the stimulating power of light (66) ; but as 

 they grow older their cuticle hardens, the stomates 

 (61) become the only apertures through which 

 vapour can fly off, and by degrees even these aper- 

 tures are either choked up, or have a diminished irri- 

 tability. As a general rule, therefore, we are autho- 

 rised to conclude that the ground should be abun- 

 dantly supplied with moisture when plants first begin 

 to grow, and that the quantity should be diminished as 

 the organisation of a plant becomes completed. There 

 are, however, some especial cases, which appear 

 to be exceptional, in consequence of the unnatural 

 state in which we require plants to be preserved for 

 our own peculiar purposes. One of the effects of an 

 excessive supply of moisture is, to keep all the newly 

 formed parts of a plant tender and succulent, and 

 therefore such a constant supply is desirable when 

 the leaves of plants are to be sent to table, as in the 

 case of Spinach, Lettuces, ancL other oleraceous 

 annuals. Another effect is, to render all parts natu- 

 rally disposed to be succulent, much more so than 

 they otherwise would be ; thus we find market-gar- 

 gardeners deluging their Strawberry plants with 

 water while the fruit is swelling, in order to assist in 

 that, to them, important operation. While, however, 

 in this case, the size of the fruit is increased by a 



