ABSORPTION IN PLANTS. 
imbibition in as hard wood as possible; and its 
success or failure in being converted into a living 
and distinct plant—provided the requisite condi- 
tions as to soil, season, and situation are attended 
to—will entirely depend on its power of main- 
taining imbibition till new organs are formed. 
If the extremity rot before rootlets are formed, 
the whole cutting will perish ; but if the extrem- 
ity drink up nourishment till rootlets have been 
sufficiently evolved to succeed them in drinking 
it up, the cutting necessarily becomes a living 
plant. Imbibition, though not a strictly natural 
process, and though confined within limits and 
subject to a comparatively speedy termination, 
thus accomplishes, for a time, all the purposes of 
absorption, and even carries them out to the re- 
sults of propagation. 
The power of imbibition by the reversed end 
of a doubly cut twig is familiar to many a youth, 
who amuses himself with sticking pieces of wil- 
lows and poplars in all sorts of ways in the 
ground, and observing how they will grow; and 
the inferiority of the power in the reversed end 
to that in the true end, is familiar to gardeners, 
who know that a cutting set in its natural posi- 
tion will usually develop the higher buds, while 
a cutting set in the reversed position will fre- 
quently develop only the lower buds. An ex- 
perimenter, who doubted whether the superior 
imbibition by the right end of a cutting in all 
the instances in which vegetable physiologists 
had recorded it might not have been occasioned 
by intrinsic though unobserved superiority in the 
cutting itself, provided himself with two branches 
of willow as nearly equal to each other in every 
property as he could determine; and, having 
placed them in water, the one with its right end 
and the other with its inverted end in the water, 
he found that the inverted branch pushed its 
roots a little more slowly than the direct one. 
But wood imbibes water, not only through its 
tissues when transversely cut, but also through 
its side pores or tissues when denuded of the 
bark. A cut branch of willow, for éxample, 
which hasall its transverse section closed up with 
gum mastic or with a thick coat of wax, and 
which is anywhere stripped of a ring of its bark 
about an inch in length, will, when immersed 
lengthwise in water, imbibe nourishment through 
the side tissues of its denuded portion, and will 
gradually form rootlets and buds, in exactly the 
Same manner as a branch inserted in water by 
its free cut end. 
Akin to the last of these phenomena, though 
essentially different from it in principle, is the 
hygrometric capacity of timber, or its power to 
take up and retain certain quantities of moisture. 
So great and constant is this hygrometric capacity, 
that every specimen of wood, when exposed to 
the air, will keep itself moist, and, when kept in 
the shade, will maintain its moisture throughout 
an indefinite period. A piece of wood was taken 
ne Count Rumford from the inner part of a 
Inch 
beam which had been about 150 years in a build- 
ing, and, on being dried by him in an oven, was 
found to lose about ten per cent. of its weight ; 
and that specimen was thought by the Count to 
have attained the greatest degree of dryness 
which any piece of timber is ever capable of ac- 
quiring in the climate of France. An oaken 
faggot, after being exposed eighteen months to 
the air, and becoming as thoroughly dry as the 
most suitable billets of any kind for fuel, was 
found, on subjection to high oven heat, to lose 
twenty-four per cent. of its weight. Hven chips 
of wood which have been dried in a stove toa 
state of complete exsiccation, will afterwards 
very freely imbibe water. A thoroughly dried 
chip of Lombardy poplar, 5 inches long, and 6 
lines broad, will, if placed twenty-four hours in a 
room, imbibe upwards of three-fourths of a grain 
of moisture; a chip of thoroughly dried oak, of 
the same size, and in the same conditions and 
situation, will imbibe one grain and two-fifths ; 
and these chips, if afterwards exposed during 
eight days to the open air, will not increase in 
weight under a continuance of the same temper- 
ature, but, on the other hand, will lose a portion 
of their weight if the temperature should rise. 
The imbibing power of wood is thus proved to 
be at once pervading, rapid, and retentive ; and 
both this power in timber, and the analogous 
but higher power of absorption in living or stand- 
ing plants, appear to co-exist with the duration 
of the vegetable tissues, or to he modified or de- 
stroyed only as these tissues suffer decay, dis- 
temper, or dissolution. 
Another power of living plants, closely resem- 
bling that of absorption, yet so far differing from 
it as to be more properly termed inhalation, is 
the power by which they take in gaseous fluids. 
The atmosphere, as we shall see in some future 
articles, has quite as much to do as soil and 
water with the nourishing of plants ; and in par- 
ticular, it furnishes matter for the formation of 
a very large proportion of the bulk or substance 
of them all in the form of carbonic acid gas, and 
matter for the formation of a considerable and 
very valuable proportion of the substance of 
many in the form of nitrogenous or ammoniacal 
gases. Since water and other non-elastic fluids 
have been proved to penetrate leaves, roots, and 
epidermis, no difficulty can exist in understand- 
ing that gases may penetrate them with equal 
or even superior facility. “It might be asked, 
however,’ observes Keith, “whether the water 
and the gases enter by the same pores, where 
pores are found to exist. But though there ap- 
pears to be nothing absurd in the assertion of 
the affirmative, yet it seems probable that each 
has its own peculiar pores or stomata. At least, 
it is known that some surfaces which repel 
moisture exhibit no evidence leading us to sup- 
pose that they repel the common air. This is 
well exemplified in the case of cabbage leaves, in 
the time of rains and dews, when the drops roll 
B 
