818 LIFE OF THE WHOLE PLANT. 
which have of late years taken place are mainly due to the in- 
creased interest taken in such matters, and the many admirable 
researches to which it has led. But however interesting in an 
agricultural point of view these applications may be, our neces- 
sary limits will not allow us to dwell upon them further. 
Section 2. LirE OF THE WHOLE PLANT, OR THE PLANT IN 
ACTION. 
The various substances required by plants as food having now 
been considered, we have in the next place briefly to show how 
that food is taken up by them, distributed through their tissues, 
and altered and adapted for their requirements. The considera- 
tion of these matters involves a notice of the functions of vege- 
tation. The more important facts connected with these functions 
have, however, already been referred to in treating of the Special 
Physiology of the Elementary Tissues, and of the Root, Stem, 
and Leaves ; so that it now only remains for us in this place to 
give a general recapitulation of the functions of the plant, and 
to consider them as working together for the common benefit of 
the whole organism. It will be convenient to treat of these 
under the two heads of (1) Absorption ; and (2) Distribution of 
Fluid Matters through the Plant, and their Alteration in the 
Leaves. 
1. Absorption.—The root, as already noticed, is the main 
organ by which food is taken up dissoived in water, for the 
uses of the plant. No matter can be absorbed in an undissolved 
condition ; and this absorptive power is owing to the superior 
density of the contents of the cells of the young extremities of 
the roots over the fluid matters surrounding them in the soil, 
leading to the production of osmotic action through the cell- 
walls (see page 781 and jig. 1139). 
That the roots do thus absorb fluid matters may be proved 
by a very simple experiment. Thus, if we take two glasses of 
the same capacity, and pour water into them until it is at the 
same level in each, and then put the roots of a vigorous 
growing plant in the one, and expose both in other respects to 
the same influences of light, heat, and air, it will be noticed 
that the water will gradually disappear from the glasses, but 
from that in which the roots are placed far more rapidly than 
from the other without them, and the more rapid removal in the 
former case must therefore be vowing to its absorption by the 
roots. In this way we can also estimate, in some degree at 
least, the amount absorbed, which will be found to be very con- 
siderable ; commonly, in a few days, far exceeding in weight 
that of the plants which are experimented upon. This absorp- 
tion of liquid by the roots is in many cases altogether inde- 
pendent of leaf-action, for, if the rootlets be healthy and the 
tissues above them filled with fluid, it will always occur ; and 
