VEGETATION AND THE ATMOSPHERE. 183 
because it draws nourishment from the air, and also because it seeks some in 
the soil. At the end of a certain period of vegetation it is gathered, and then 
we ascertain by new chemical analyses, first, how much carbon, oxygen, hy- 
drogen, and azote it has gained; secondly, how much of those substances the 
soil has lost—that is, how much it has given up to the plant. The difference 
is due either to the air or to the water. That settles the account, and event- 
ually the balance of profits and losses. 
The application of this method, as rigorous in its conception as dificult in 
its practice, has disclosed a first fact of the same order as the decomposition of 
carbonic acid. All the plants have acquired an excess of hydrogen which 
comes to them not from the soil or the air, neither of which contains any ; it 
has; therefore, of necessity, been derived from the water. Plants, then, do not 
limit their action to separating oxygen from carbon; they also divorce hydro- 
gen and oxygen, retaining the first, expelling the second. The water was hy- 
drogen burned, as the carbonic acid was carbon consumed; in both cases the 
plants have destroyed the effects of the combustion by delivering up the com- 
bustible bodies in the state in which they were before they were burnt. In 
verifying this action, finally exerted on the water, it has not been ascertained 
when it is effected or in what organs accomplished. 
A second consequence flows from the analyses of M. Boussingault, namely, 
that every plant arrived at maturity has gained azote, which is deposited chiefly 
in its seeds ; and as this azote may come either from the air which contains it 
in a free state, or from manures which have communicated it to the soil, it was 
necessary to institute special experiments to determine its origin. M. Boussin- 
gault proceeded as follows: he first sowed trefoil (clover) ina soil formed ex- 
clusively of calcined sand, which could only furnish to the plant mineral sub- 
stances and the pure water with which it was moistened ; as to azote, it con- 
tained none. Under these exceptional conditions the trefoil still completed all 
the phases of its vegetation, and in the end it had acquired a small but positive 
proportion of azote, which necessarily came from the air. The Jerusalem arti- 
choke gave the same result with greater distinctness. After having matured, it 
. contained twice as much azote as the seed from which it sprang; but when the 
attempt was made to reproduce the experiment with cereals, and above ail 
with wheat, it was found that the azote of the grain was carefully preserved, 
but had in no degree augmented. 
In all these cases the vegetation of the plants was extremely embarrassed, 
none of them having the aspect of healthiness which is witnessed in rich soils; 
the artichoke, however, suffered less than the trefoil, and this less than the 
wheat, which could not advance so far as to mature its grains. 'The reason of 
this is evident—azote was wanting; all plants need it, the cereals exact it, and 
when they do not find it in the soil they languish and often die. In order to 
confirm this conclusion M. Boussingault submitted to a comparative trial three 
plants of Aelcanthus placed in three exactly similar pots, filled with pure sand 
and moistened with pure water. The first received no manuring, but to the 
second were supplied eight centigrammes, and to the third sixteen centi- 
grammes of azotate of potash. From the first days the plants exhibited the 
difference of the tre:tment to which they were subjected. The first languished 
and died; the second vegetated, but remained sickly; the third was remarka- 
ble for its fine health. At maturity, the second had borrowed from the soil 
four centigrammes of azotate of potash, and the third eight. But what was 
chiefly remarkable was, that duriug its progress the last decomposed twice as 
much carbonic acid as the second. The azote thus performed the part of ex- 
citing the other functions and of giving to the subject which receives it, or of 
taking away from that which is deprived of it, the vitality without which it 
could not act upon the atmosphere. 
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