The Life of the Plant. ; 163 
plants, which are provided with a great number of hairs or 
with a root-sheath, the whole surface of the root appears to 
possess the power of absorbing nutrient substances in the 
form of vapour. 
In addition to the roots, ithe higher plants possess also 
in the leaves organs which are adapted for the absorption of 
nutrient substances in a gaseous condition. But experimental 
observation has shown that the leaves, even under favourable 
circumstances, do not absorb fluid nutriment, either in the 
form of drops or of vapour, so as to carry it to the other 
parts of the plant.! 
: Since the nutrient substances must pass through. the 
closed walls of the cells in order to reach their interior, it 
follows that they must be present in a dissolved fluid or 
gaseous form. They are then received into the cells 
adapted for this purpose by means of osmose; since there 
are in general two fluids, the cell-sap and the water ab- 
sorbed from the soil, capable of mixing with one another, and 
separated only by the permeable cell-wall. ‘The absorption 
of nutriment is, therefore, only a eens of two fluids of 
different densities. 
The terms osmose, diosmose, and dzffuston have been given to the 
mingling of fluids through a permeable partition-wall, z.e. one which 
has no visible perforations. If, for example, a vessel closed below by 
an animal membrane (Fig. 344 4) is filled with a concentrated solution 
of cupric sulphate (blue vitriol), and is then immersed in a vessel filled 
with water (z), the water will pass gradually through the bladder into 
the vessel 4, and the fluid will rise in a tube 7 attached to it, while the 
level at z falls. If, on the contrary, the cupric sulphate were placed 
outside, and the water within the vessel 4, the fluid would fall in the 
tube 7, while the level 72 would rise. In both cases a small quantity of 
the cupric sulphate also passes through the bladder into the water, as 
| [An exception to this law seems to exist in the case of the ‘ car- 
nivorous plants’ on whose habits Mr. Darwin has thrown so much 
light, such as Drosera, Pinguicula, ana Nepenthes, which appear to 
have the power of absorbing nitrogenous substances through their 
leaves, and digesting them within their tissues.—ED. ] 
M 2 
! 
\ 
