groups or species of vegetables, has long been a 
favourite subject of theory on the part of many 
scientific writers, and a prolific source of bewil- 
derment on the part of almost all their practical 
readers. Passion for theory, or the mere poetry 
of science, has generally occasioned inquirers to 
confound a few resemblances on the very out- 
skirts of the two kingdoms, or a similarity be- 
tween one or two phenomena of certain species, 
with a true and pervading analogy. The real 
analogies which exist, and which alone can give 
light to science or assistance to practice, seem to 
be too few and commonplace for the abstruse 
purposes of theorists; and the unreal analogies, 
which are suggested by resemblance or created 
by fancy, appear to possess an absurd charm in 
their very incomprehensibleness by plain men, 
and total want of all possible adaptation to any 
purpose of utility. Any of our practical readers 
who cannot understand the analogies between a 
| buffalo and an oak-tree, between a snail and a 
hyacinth, between a sheep and a rose-bush, or 
between a jelly-fish and a bean-plant, may assure 
himself that he will suffer no detriment from his 
ignorance. 
All animals and all vegetables possess life; all 
have organization; all elaborate great chemical 
changes in their interior organism; most grow 
or enlarge their substance by assimilating ali- 
mentary matters obtained from without; many, 
perhaps most, throw off, in an excrementitious 
manner, such proximate elements as are unsuited 
to their own substance; most vegetables and 
nearly all animals, propagate their respective spe- 
cies by fecundation; the epitome of any pheeno- 
gamous plant, when buried as a seed in the soil, 
rots and reproduces the whole plant, and the epi- 
tome of the human body, when buried in its final 
terrestrial form in the earth, rots and will event- 
ually rise again in glory ;—these are true analo- 
gies, and they afford exquisite mutual illustra- 
tions of the constitution of the two great classes 
of organized bodies. But they are not at all 
the kind of analogies with which imaginative 
physiologists have wished to entertain their 
readers. 
One favourite analogy with theorists is be- 
tween the circulation of the sap in plants and 
the circulation of blood in animals. But this is 
a mere play upon a word. The motion of liquid 
within a plant is simply the ascent of sap and the 
descent of cambium,—the free ascent of the liquid 
in one form, and the fixational descent of it in 
another form. We speak of the circulation of 
moisture in the soil, when we mean merely the 
descent of rain-water and the ascent of aqueous 
vapour; and we speak, in a precisely analogous 
manner, of the circulation of sap in plants; but 
we do not imagine, for a moment, that these are 
true circulations; nor ought we, for an instant, 
to compare them with the constant circulating 
flow of the slowly changing vital blood in an ani- 
mal. Yet a highly distinguished phytologist of 
ANALOGY. 
161 
the present day assumes, first, that the ascent of 
sap and the descent of cambium are the same 
phenomenon as the circulation of blood,—next, 
that the flow of the sap and the cambium forms 
all organs and wields the power of all organic 
functions,—next, that sap constantly rises by 
capillary attraction, when any proper force is at 
work for removing obstructions from the top of 
the capillary tubes,—and next, that a precisely 
proper force of this kind is in constant action in 
the chemical play which goes on within the leaf; 
—and on this most unphilosophical series of as- 
sumptions, all based on the fancied analogy be- 
tween vegetable and animal circulation, he erects 
the monstrous doctrine, that life is a chimera of 
the dark ages, and that what we usually desig- 
nate life is only a combination of capillary attrac- 
tion and simple chemical action! How dismally 
and most humblingly true does it continue to be, 
that “the world by wisdom knows not God!” 
Another favourite analogy is between the al- 
leged respiration of plants and the true respira- 
tion of animals, or between the functions of leaves 
and the functions of lungs. But the leaves of 
plants elaborate the sap brought up to them from 
the roots, and bring a portion of it into a condi- 
tion of fitness to be incorporated with the plant’s 
substance ; and, in this office, they are vastly 
more analogous to a stomach than to lungs ;— 
and in so far as they operate with atmospheric 
air, they in fact achieve the very reverse of the 
result which is worked out by the lungs of ani- 
mals; for they take in the carbonic acid of the 
atmosphere, abstract its carbon, and give back 
its oxygen; while animal lungs take in the oxy- | 
gen of the atmosphere, combine it with liberated | 
carbon from the blood, and give back carbonic 
acid to the atmosphere; and indeed these reverse 
and entirely unanalogous processes constitute the 
principal and most beautiful contrivance by which 
the wisdom of the all-beneficent Deity preserves 
unimpaired the purity of our atmosphere, and 
maintains the balance of animal and vegetable 
forces in our world. The fact that both leaves 
and lungs operate on atmospheric air, is no more 
a ground of analogy, than the fact that all sub- 
stances in the processes of oxidation, combustion, 
fermentation, and putrefaction also operate upon 
atmospheric air. A stagnant pond or a fen, in 
particular, might, with far more truth than leaves, 
be alleged to breathe; for it does exactly that to 
atmospheric air which is done to it by animal 
respiration. 
The two examples which we have stated suffi- 
ciently illustrate the fallaciousness of the analo- 
gies which are commonly instituted between the 
functions of plants and the functions of animals ; 
and a very brief example or two may equally ex- 
hibit the character of those which are commonly 
instituted between the organic structure or the 
entire economy of the two kingdoms.—One anal- 
ogy is instituted between seeds which are long 
in a dry condition, and afterwards germinate 
L 
