DIFFERENT ABSORBING POWERS OF THE TWO SURFACES. 179 



confined within pots. The luxuriance which such plants often 

 exhibit, sufficiently proves, that the atmosphere contains all the 

 materials, which are necessary for the growth even of the highest 

 plants ; and that, if the structure is adapted to imbibe them from 

 it, no other kind of supply is necessary. 



273. A fact familiar to every one, who has bestowed common 

 notice on the processes of vegetation, equally proves that the 

 leaves, as well as the roots, are capable of absorption. "When 

 plants are faded by the intense action of light and heat, and have 

 suffered from deficiency of water, they are observed to revive 

 rapidly, when their surfaces are moistened, even if no fluid have 

 been supplied to the roots. More precise experiments lead to the 

 same result. It has been found that leaves placed with one of 

 their surfaces upon water, would remain fresh for several months ; 

 the absorption through it counterbalancing the transpiration 

 through the other. From a considerable number of experiments 

 on different kinds (though this, again, is a subject which any one 

 may investigate with great ease, and with the certainty of arriving 

 at new and interesting results with a very little trouble), it seems 

 to be ascertained, that the leaves of trees and shrubs retain 

 their verdure longest, when the lower side is placed in contact 

 with water ; whilst the leaves of herbaceous plants absorb most 

 readily by their upper surface, or in an equal degree by both. 

 Thus, leaves of the White Mulberry, placed with their upper 

 side in water, faded on the fifth day ; whilst those which absorbed 

 by the lower surface, remained fresh nearly six months. This 

 effect, however, was no doubt due in part, to the greater degree 

 of obstruction to the loss of fluid by transpiration, in the second 

 case than in the first ; the stomata being principally situated on 

 the lower surface. But in experiments on other plants, in which 

 they are similarly disposed, the contrary result has been observed. 

 Thus, leaves of the Nettle, whose inferior surface only was kept 

 moist, faded at the end of three weeks ; whilst others whose 

 upper surface was in contact with water, lived for two months. 

 Lastly, the leaves of the Sunflower, Kidney-bean, Cabbage, and 

 of many other plants, were observed to remain fresh for the same 



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