280 Vegetable Physiology. 



Nettle, whose inferior surface was only kept moist, faded , 

 the end of three weeks, while others whose upper surface wa 

 in contact with the water, lived for two months. Lastly ri 

 leaves of the Sunflower/ Kidney-bean, Cabbage, and man 

 other plants, were observed to remain fresh for the same length 

 of time, by whichever of their surfaces they received their sun- 

 ply of fluid. 



The absorbing power of leaves has been shown by other 

 satisfactory experiments. Some plants of Mercurialis (M e , 

 cury) were placed in water, some of them being immersed bv 

 their roots, and others touching it by a part of their leaves 

 alone, a small shoot of each being left out, for the purpose of 

 comparison with the rest. After five or six weeks, the shoots 

 of the plants which were nourished by the leaves, differed little 

 in vigor from those which had been supplied by the roots 

 Experiments upon single leaves, which have already partially 

 faded, are still more striking. Some leaves of rotamo(rp,t on 

 natans (Pond-weed) after being wiped dry, were weighed' 

 and after remaining out of the water for two hours, they were 

 found to have lost from three and a half to five and a half 

 grains each. They were then put in water, and after the lapse 

 of two hours more, were again wiped dry and weighed. It 

 was found that they had severally gained from three to five 

 grains each ; and this increase, which was also evident from 

 the restoration of their natural freshness and plumpness, could 

 only have taken place by absorption through the cuticle, as the 

 cut ends of their footstalks were defended by soft cement. 

 Many similar experiments might be mentioned, but these are 

 sufficient to show that leaves whose tissue has been deprived 

 of fluid, have the power of replacing it by absorption from 

 water, or from a moist atmosphere. This absorption appears 

 to take place chiefly through the membrane of the cuticle, but 

 more particularly by the downy hairs, which seem to act like 

 so many root-fibres. They are chiefly developed in plants 

 which grow in situations much exposed to the light, and to a 

 dry atmosphere, whilst the same species in damp, shady situa- 

 tions, will not form them. It has been noticed that they lift 

 up their points and separate from one another at the approach 

 of the evening dew, which collects in minute drops around 



