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THURSDAY, NOVEMBER 28, 1872 
* FERMENTATION AND PUTREFACTION* 
: 1? is one of the great attractions of the science of 
4 Botany, an attraction common to all the other 
_ branches of the study of Nature, that wherever we may 
_ happen to be, and under whatever circumstances, some- 
thing interesting and suggestive is continually brought 
before the eye and mind educated to understand its 
teachings, and no true naturalist ought long to be in a 
difficulty seeking for a suitable subject for illustration. 
At this season of dearth of flowers I hold in my hand a 
basket of “Duchesse” pears. These have, after their kind, 
been plucked in France before they were ripe, and some 
few of them are hard, green, and flavourless ; others are 
soft, full, and mellow, with a rich, delicate aroma—morsels 
fit for the gods—while others have gone too far,and show 
® the 
¥ —“‘little pitted speck on garner’d fruit, 
That rotting inward slowly moulders all.” 
If you will allow me, I will, during the few minutes still 
at my disposal, give you a brief sketch of what has been 
done of late towards the explanation of the two pheno- 
mena which are for the moment the most prominent in 
connection with these pears, their ripening, and their 
decay. 
“These changes depend upon fermentation and putrefac- 
_ tion, two processes which are very familiar, and which 
have of late engaged the attention of some of the most 
_ able and skilful men of science, both on account of their 
_ vast importance in the economy of nature and of art, 
and of the singular phenomena which accompany them. 
_ These phenomena are very complex and difficult ; but 
_ chiefly through the patient researches of botanists such 
as De Bary on the one hand, and of chemists and phy- 
_ siologists who may be represented by Pasteur, Lister, 
_ Burdon Sanderson, and Hartley on the other—steady 
progress is undoubtedly being made towards their solu- 
tion, although much still remains obscure. 
_ The character which most broadly distinguishes the vege- 
table from the animal kingdom is certainly the power which 
_ the former possesses when taken in mass of winning over 
from the inorganic kingdom binary compounds which can- 
hot contribute directly tothe nutrition of animals, decompo- 
sing them, and re-combining their elements into organic 
compounds suitable for the support of animal life. This 
process—the decomposition of water into oxygen and 
hydrogen, of carbon dioxide into carbon and oxygen, and 
_ of ammonia into hydrogen and nitrogen, and the re-com- 
bination of these four elements while in a nascent condition 
into starch, sugar, gum, protoplasm, &c.—is, so far as we 
_ Know, carried on in plant-cells containing endochrome 
under the influence of light, and in such cells and ‘under 
such circumstances alone. We thus find that this truly 
vegetable process is performed by a very small portion of 
an ordinary plant. The cells of the internal organs of 
plants and of large pulpy masses, such as these pears, 
_ connected with the function of reproduction, are perfectly 
colourless ; simple sacs of cellulose, containing in their 
* From the Opening Address for the Session 1872-73 to the Botanical 
Society of Edinburgh, delivered on Nov. 14, by Prof. Wyville Thomson, 
F RS., President of the Society. 
No. 161--von, vit. 
PEN 
NATURE 
61 
early condition protoplasm, and increasing and multiply- 
ing by its agency; and afterwards containing other 
substances in addition, such as starch and sugar, the 
products of its assimilation and excretion. These masses 
of protoplasm with their investing membranes composing 
the so-called “cells” of the pear, feed, indeed, upon the 
ternary and more complex compounds produced by the 
leaves of the pear tree, and are aérated by the fluids which 
are passing through the tissues of the pear tree; but, 
secluded fromthe light, and developing no special colouring © 
matter, their reactions are not in the strict sense “ vege- 
table ;” they absorb the organic compounds and breathe 
the distributed air in the true animal sense, just as Amebe 
would do, To take the function of respiration as a test, 
they absorb oxygen and exhale carbon dioxide, while in 
the green parts of plants, which alone perform the great 
function of the vegetable kingdom in keeping up the 
“balance of organic nature,” the exhalation of carbonic 
acid is in the sunshine entirely masked by the exhalation 
of oxygen—the product of its decomposition. A green 
tree may be likened to that wonderful animated tree, one 
of the oceanic Siphonophora, where a certain set only of 
the polyps are set aside to feed and to supply nutrition 
for the whole, while others, identical with these in essential 
structure, feel, or sting, or reproduce the species, or palpi- 
tate through the water as locomotive swimming-bells. 
It is, perhaps, not easy at once to realise this difference 
in the vital relations of the different parts of the same 
plant, but it becomes clear enough in the case of pale 
parasites, for example Czscwéa. The dodder possesses no 
endochrome cells of its own ; it feeds like an animal upon 
the organic compounds elaborated by its host. It con- 
tributes in no way as a vegetable to the balance of 
organic nature, and yet it is evidently a plant nearly 
allied to the ordinary bird-weeds, with all the characters 
of their well-known natural order. 
These “ Duchesse” pears are separated from the tree. 
They were probably separated physiologically before 
they were taken off, for before we would consider them 
fully ripe a certain shrivelling takes place in the cells and 
vessels of the fruit-stalk at a kind of joint, and the com- 
munication between the pears and the tree is at first 
partially and then entirely interrupted. But the pear does 
not die; it hangs out in the sunshine, and certain chemical 
changes take place within it, still under the guidance of 
vital action, sweetening it and developing its favour. We 
learn from the beautiful researches of M. Bérard that if 
fruit be placed to ripen in air or in oxygen gas, a consider- 
able quantity of oxygen is absorbed and an equivalent 
proportion of carbon dioxide is given off; that, in fact, 
a notable quantity of oxygen is burned in a true process of 
respiration. It is calculated by De Bary that the number 
of plants in which chlorophyll is absent—that is to say, 
which have no power of decomposing and re-combining 
the elements of water, carbon dioxide, and ammonia, 
and which consequently require to have their food pre- 
sented to them in the form of organic matter—is fully 
equal to that of green plants, say 150,000. These plants 
are chiefly fungi. The part they play in the economy of 
the organic world is wonderful. The moment a plant 
gets worsted in the battle of life, becomes delicate from 
uncongenial soil or other circumstances, or gets smothered 
by a more vigorous rival, they set upon it and burn it. 
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