184 VEGETATION AND THE ATMOSPHERE. 
Now, be it remarked, a plant contains more than the half of its weight of 
carbon and only some thousandths of azote. For what, then, does this sub- 
stauce serve in vegetation, which is so necessary to it, although introduced in 
so weak a proportion? M. Payen will téach us. According to this skilful 
chemist, all the organs of vegetables commence by an azotized matter analo- 
gous to fibrine, to which are added by little and little the cellular and fibrous 
tissues which, in expanding, produce the entire plant. This fibrine is never 
destroyed, is found in all its organs, and is thus the rudiment of all the parts 
of the plant, which cannot be developed without it, and consequently without 
the azote, which is its essential base. In fine, plants are composed of carbon, 
water and hydrogen in excess; they contain besides a fourth simple body, 
azote, which occurs in a very minute proportion, but whose presence is essen- 
tial to life. The atmosphere furnishes carbon in abundance; water, that is to 
say oxygen and hydrogen, is given by the rains; azote is required from the 
soil, and as it is rare therein we introduce it under the form of manure. It is 
the great care of the agriculturist; it is the heaviest, the most indispensable, 
and the host productive of his expenditures. 
Ill. 
Notwithstanding the important knowledge which we possess on the subject 
under consideration, it is still impossible not to recognize on many points the 
insufficiency of our information. That which is most inexplicable in our world, 
that which should most awaken our curiosity and invite our researches, is the 
great physiological fact of which I have related the discovery. The chemists 
have assiduously studied carbonic acid; they know all the properties it pos- 
sesses: they can foresee all the reactions which it occasions or undergoes in 
the conditions in which it pleases them to place it; they are ignorant of none 
of the circumstances which produce it or destroy it; but they have never seen 
it steadily decomposing under the influence of light in the presence of some 
inorganic matter, and yet, what they cannot effect, the smallest leaf shone upon 
by the sun produces instantly with a rapidity and abundance which the 
naturalist regards with admiration. In ten hours an aquatic plant yields fifteen 
times its own volume of oxygen; a single leaf of the water-lily diffuses 300 
litres during each summer; and M. Boussingault having directed into a vase 
filled with vine leaves, in the sun, a current of carbonic acid, received on its 
exit only pure oxygen. Now we are obliged to acknowledge that this fact, so 
common, so easily accomplished by the leaves at every hour of the day, chem- 
istry can neither comprehend nor imitate. 
If we cannot understand and imitate the conditions of a fact relatively so 
simple and so definite, what must not be our embarrassment when we would 
analyze the chemical and physiological phenomena which ensue from it? We 
seé in effect three simple bodies, and rarely four, combine in relations indefi- 
nitely variable in order to give rise to the most numerous and different com- 
pounds—wood, starch, sugars, oils, wax, balsams, essences, both fragrant and 
offensive, delicious fruits and violent poisons, acids like vinegar, and alkalis 
like quinine or strychnine, coloring or colorless substances—in a word, products 
whose infinite variety transcends the dreams of imagination. Not without dis- 
may must we measure the depth of our ignorance in the presence of phenomena 
so multiplied, and whose mechanism escapes us so absolutely. 
There are, however, ill-disciplined minds which wish to explain everything, 
especially what they are most ignorant of. It has been said that plants proba- 
bly contained compounds of carbonic acid and of azote, formed at night and de- 
composed in the light during the day; it has been also said that there exists 
in green leaves a sort of fermentation deriving its activity from the sun, and 
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