16 ABSORPTION 
quire to be proved or illustrated by experiment 
and argument, but is clearly evinced by three 
classes of facts which occur under almost every 
person’s observation, and are perfectly intelligible 
to the humblest understanding,—the fall of thick 
vapours, the fall of rain, and the artificial water- 
ing of plants. When a fog or a heavy dew occurs 
after a long drought and previous to the fall of 
rain, drooping and sickly plants begin to revive 
and te resume their verdure, in the total absence 
of any penetration of moisture to the soil around 
their roots; and when gentle rain descends, or a 
light artificial watering is given, they in the same 
way exhibit obvious appearances of freshening 
and invigeration, before the moisture has time to 
affect them otherwise than through the leaves, 
or, at the utmost, through the epidermis of the 
branches and the stem. The sudden arresting of 
exudation or transpiration of the juices within 
the plant by the stopping up of the pores or sto- 
mata of the leaves, might probably be assigned 
by some persons as an explanation of the refresh-. 
ing or revival; yet though both this, and some 
degree of absorption through the pores of the 
epidermis, may be admitted to operate, they 
clearly cannot possess sufficient force to produce 
the whole breadth of the phenomena; and the 
main cause must be sought, where even a care- 
less onlooker may almost imagine himself to see 
it, in the absorption of the leaves. 
The moisture, then, which a plant requires for 
its nourishment, is received partly through the 
pores of the epidermis of the stem, the branches, 
the fruit, and the hard parts of the root,—partly 
through the spongioles at the extremities of the 
radicles,—and partly through the stomata or 
little mouths of the leaves and the flowers. The 
quantity of liquid taken up from the soil, or 
drank in from the atmosphere, very widely varies 
in different conditions of the weather, at differ- 
ent seasons of the year, and at different stages in 
the life of the plant; but its varying amount 
seems much less closely connected with the pro- 
cess of absorption than with that called the ascent 
of the sap. See Ascent. The quantity of liquid 
absorbed is much greater during the play of light 
and heat than during the period of darkness,— 
much greater during the succulency of both soil 
and plant than during the prevalence of aridity, 
—much greater in spring than in autumn,—in- 
calculably greater in spring than in winter,— 
much greater during the evolution and vigour of 
the leaves than during their ripeness and mel- 
lowing,—and much greater during the period of 
the whole plant’s most rapid growth than during 
the period of its old age and incipient decay. 
The vast preponderance of a very few ingredients 
in constituting the body or bulk of all vegetables, 
proves that absorption, as to the substances which 
it takes in, is nearly uniform throughout the 
vegetable kingdom ; and yet the diversified action 
of manures, the widely different respects in which 
different plants exhaust the soil, and the capa- 
IN PLANTS. 
bilities which all land possesses of bearing differ- 
ent plants in succession after being sickened with 
each preceding one in the series, evince a degree 
of differences in absorption of the highest im- 
portance to the purposes of cultivation. 
A phenomenon, closely resembling absorption, 
yet so far differing from it as to be more properly 
termed imbibition, is exhibited by cut plants, 
whether soft or hard, fleshy or fibrous, but par- 
ticularly the woody. When the cut extremity of 
the cut branch of a tree is placed in water, it 
drinks up, through the tissues or tubes of the 
wood, a sufficient quantity of water to preserve, 
for a considerable time, the life and freshness of 
the whole plant; and though it will not renew 
itself or maintain its own health like a root, but 
will alter and rot under the action of the water, 
yet it can again and again be artificially renewed 
by the simple slicing away of as much of it as 
alters and rots, and, at each artificial renovation, 
it will present an active surface to the water, 
and will begin to imbibe the water with nearly 
as refreshing an effect to the whole branch as at 
the beginning of the experiment. If a small 
shrubby plant be lifted out of the ground, and 
cut into three parts, respectively roots, stem, 
and head, each of these parts, when its lower ex- 
tremities is placed in water, will drink up a cer- 
tain quantity of the liquid, and the head, or | 
branched and leafy section, will drink up the | 
most. If the cut extremities of two cut branches 
of raspberry, the one free or open over its section 
and the other covered with wax, be placed in 
water, and exposed to the sun’s rays, the former 
will imbibe one hundred and fifty grains of the 
liquid, while the latter will imbibe only eight ; 
and if the one whose section is covered with wax, 
first have only its extremity placed in the water, 
and next be totally plunged or immersed, it will 
imbibe no more by immersion than by mere con- 
tact,—thus rendering it probable that, in some 
cases, absorption through the pores of the epider- 
mis is very inconsiderable. A branch of a tree, 
first severed from the stem and then deprived of 
its own top, will imbibe water at either end,— 
either when placed invertedly in the water, or 
when placed in its upright or natural position ; 
yet it imbibes rather more freely, and lifts the 
water a little higher, in the latter position than 
in the former. 
The phenomena of imbibition are obviously 
those of the rooting or propagating of the woody 
sorts of plants by cuttings or slips. A proper 
cutting requires to have a clean section, that the 
tubes or tissue may be fully in contact with the 
liquid nourishment in the soil; it requires also 
to have one or more eyes or joints for the de- 
velopment of roots below the surface of the soil, 
and one or more for the development of leaves 
and branches above it; and if it be a prime cut- 
ting, it will be a twig of new wood upon a knee 
of older wood, so as to have the portion for de- 
velopment as soft as possible, and the section for 
