LIFE OF THE WHOLE PLANT.—ABSORPTION, 819 
the great force of the action in stumps cut off a little above the 
ground is well seen in such experiments as those of Hales (see 
page 822) and Hofmeister. But nevertheless, as a general 
rule, the amount of fluid absorbed by the roots is directly 
dependent upon the activity with which the other processes of 
veyetation are carried on, and more especially by the quantity 
of fluid matters transpired by the leaves ; indeed, under ordinary 
conditions, absorption is directly proportioned to transpiration 
in a healthy plant, for as fluid is given off by the leaves, it is 
absorbed by the roots to make up for the deficiency thus pro- 
duced, and therefore all stimulants to transpiration are at the 
same time exciters of absorption. (See page 821). When absorp- 
tion and transpiration differ greatly in amount, the plants in 
which such a want of correspondence takes place become un- 
healthy ; thus when transpiration is checked from deficiency of 
light, as when plants are grown in dark places, the fluids in 
them become excessive in amount ; whilst if the atmosphere be 
too dry, as is the case when plants 
are grown in the sitting-rooms of 
our dwelling-houses, transpiration is 
greater than absorption, and hence 
they require to be frequently supplied 
with water. 
The mutual dependence of ab- 
sorption upon transpiration should 
also be borne in mind in the process 
of transplanting trees. Transpiration 
is greatest at those seasons of the 
year when plants are most abundantly 
covered with leaves, and when solar 
- light is most intense ; we ought not, 
therefore to transplant at such pe- 
riods, because, as it is almost impos- 
sible to do so without some injury to 
the extremities of the roots, the 
amount of fluid absorbed may be in- 
sufficient to compensate for the loss 
by transpiration, and hence the plants 
Fig. 1149. Diagrammatic vertical 
section of the stem of a Dicoty- 
ledon showing the distribution 
of the sap. The direction is 
indicated by the arrows. a, a. 
Roots, by which the fluid mat- 
ters are absorbed. 6,6. The 
tissues by which they ascend 
to the leaves, c,c. d,d. Outer 
portions of stem and inner bark 
where the descent takes place. 
é. Vertical section of a branch. 
will languish, or die, according to 
circumstances. By transplanting in 
autumn or spring, we do not expose 
the plants to such unfavourable con- 
ditions, as the light is then less intense, and there are no leaves 
from which transpiration essentially takes place. (For further 
particulars on Absorption, see Absorption by the Root, page 790. ) 
2. Distribution of Fluid Matters through the Plant, and their 
Alteration in the Leaves.—The fluid matter thus absorbed by the 
roots (the sap, as it is called) is carried upwards by their tissues 
(fig. 1149) to the stem, and through its young portions to the 
3G 2 
