OF LEAVES. 



41 



top of which he placed a number of leaves, some 

 having the uppur, and others the under surface 

 applied to the water, so as that they only floated 

 in it, but were not immersed. If the leaf re- 

 tained its verdure longest with its upper surface 

 applied to the water, the absorbing power of the 

 upper surface was to be regarded as the greatest ; 

 but if it retained its verdure longest with the 

 under suiface applied to water, then the absorb- 

 ing power of the under surface was to be regarded 

 as the greatest. The experiment was made in 

 the spring and autumn, the temperature being 

 between five and ten of Reaumur, and the leaves 

 employed being such as were fully expanded. 

 The result was as follows. Out of fourteen 

 lierbs, of different families, selected for the pur- 

 pose of experiment, the leaves of six — the wake- 

 robin, kidney bean, sun flower, cabbage spinach, 

 and small mallow, were indifferent to the mode 

 in which they were applied to tbe watT, and 

 were found to retain their verdure equally long, 

 whether moistened by the upper or under surface. 

 The rest, the plantain, white muUein, great mal- 

 low, nettle coxcomb, purple leaved amaranth, 

 marvel of Peru, and balm were not indifferent 

 to the mode in which they were applied to the 

 water, but retained their verdure longest when 

 moistened by the upper surface. The following 

 are the most remarkable examples of the relative 

 capacity of the different surfaces. The leaf 

 of the nettle, when moistened by the upper sur- 

 face, lived two months ; but when moistened by 

 the under surface, only three weeks. The leaf 

 of the amaranth, when moistened by the upper 

 surface, lived three months ; and when moistened 

 by the under surface, only seven or eight days. 

 The leaf of the mullein, when moistened by the 

 upper surface, lived five weeks ; and when 

 moistened by the under surface, only five days. 

 A leaflet of the French bean absorbed also a 

 sufficient quantity of moisture to nourish 

 another leaflet that was still attached to the same 

 footstalk, though not touching the water. Out 

 of sixteen trees, or shrubs, of different kinds, 

 selected for the purpose of experiment, the leaves 

 of only two, the lilac and aspen, retained their 

 verdure equally long, by whatever surface they 

 were moistened. But the leaves of the others ; 

 the vine, pear, cheiTy, px-une, apricot, walnut, 

 mulberry, oak, hazel, rose, &c., retained it longest 

 when moistened by the under surface. The 

 following are the most remarkable examples of 

 relative capacity. The leaves of the white 

 mulberry, when moistened by the under surface, 

 retained their verdure for nearly six months ; 

 but when moistened by the upper surface, they 

 retained it for only five or six days. The leaves 

 of the vine, poplar, walnut, faded almost as soon 

 when moistened by the upper surface, as when 

 left without water altogether. The leaves of 

 tlic hazel and rose, when moistened by the under 



surface, absorbed a suflicient quantity of mois- 

 ture to nourish also other leaves on the same 

 branch, though not touching the water. But as 

 the foregoing experiments on leaves were made 

 on such only as were detached from the plant, 

 it may be said that they are not well calculated 

 to become the ground of any general conclusion ; 

 and that they do not represent to us what ac- 

 tually takes jjlacc in growing vegetables. But 

 if we appeal to the actual facts which take 

 place in nature, we shall find that they are con- 

 firmatory of the above experiments. If after 

 a long drought a fog happens to take place be- 

 fore any rain fall, so as to moisten the surface 

 of the leaves, the plant begins to revive, and to 

 resume its verdure long before any moisture can 

 have penetrated to the root. Hence, it follows 

 incontestibly that moisture has been absorbed 

 by the leaf, because it is impossible to account 

 for the change that has been effected, except by 

 such absorption. But the efficacy of rains 

 themselves, and of artificial waterings, may be 

 accounted for upon the same principle ; for they 

 have not always penetrated to the root when 

 they are found to liave given freshness to the 

 plant; and, indeed, many plants will thrive 

 merely by having their leaves kept moist, though 

 no water should reach the root at all. The same 

 thing might be said of the immersed /mc«, many 

 of which, being totally destitute of root, and 

 constituting merely a sort of frond or leaf, ab- 

 sorb the nourishment necessary to their support 

 by the whole of their surface. The moisture 

 then entering the plant as food, is taken up by 

 means of the absorbent pores of the epidermis, 

 not only of the root and leaf, but often, as may 

 be presumed, of the other parts of the plant also, 

 at least when they are in a soft and succulent 

 state. Bonnet has shown that most leaves ab- 

 sorb moisture better by the one surface than 

 the other; and it is known that some surfaces 

 do actually repel it, as may be seen in the leaves 

 of the common cabbage, after a fall of rain or 

 dew, when the drops roll along the upper sur- 

 face without wetting it, or lodge in its folds and 

 hollows, like globules of quicksilver. This is 

 the case also with all such plants as are covered 

 with bloom. It is probable, therefore, that all 

 such surfaces as repel moisture, are fitted rather 

 for the inhalation of air. Grew first established 

 the importance of air to the life of plants, and 

 conjectured that it was absorbed by the leaf. 

 Papin, with a view to ascertain the point in ques- 

 tion, introduced into the receiver of an air pump 

 an entire plant, root, stem, and leaf. The con- 

 sequence was, that on the exhaustion of the air, 

 the plant very soon died. He then introduced 

 a plant by the root and stem only, while the 

 leaves were still exposed to the influence of the 

 air. In this case, the plant lived much longer 

 than in the former, and warranted him, as ho 



