224 
THE CABINET OF NATURAL HISTORY 
as are yet higher ; the leaf-stalk and leaf, the flower-stalk 
and flower ; as well as in the herb also, and in the lofty 
palm, in which no such plates exist? Here it will be ne- 
cessary to introduce the agency of a new cause, to com- 
plete the work that has been thus begun, and of a new set 
of machinery to supply the deficiency or absence of the ma- 
chinery that has been already invented. 
How unsatisfactory the best of these theories is, must be 
self-evident, even to persons unacquainted with the struc- 
ture of vegetables. Du Petit Thouars has, therefore, pro- 
posed a new hypothesis, which to us seems by far the least 
objectionable. He dismisses the question of the mechanical 
action by which the motion of the sap is maintained; think- 
ing, with much justice, that no principle of physics, with 
which we are acquainted, is sufficient to explain it, and he 
therefore attributes the mere motion to an inherent power, 
with which nature has been pleased to endow vegetables. 
But the cause of the renewal of its motion in the spring, 
after remaining in a quiescent state for several months, he 
ascribes to the necessity of maintaining a perfect equi- 
librium in the system of a plant. So that, if a consumption 
of sap is produced at any given point, the necessity of 
making good the space so occasioned, consequently throws 
all the particles of sap into motion, and the same effect will 
continue to operate as long as any consumption of sap takes 
place. The first cause of this consumption of sap he de- 
clares to be the development of the buds, and already 
formed young leaves, by the stimulating action of light and 
heat, but particularly of the latter. As soon as this deve- 
lopment occurs, an assimilation and absorption of sap is 
occasioned, for the support of the young leaves; a vacancy 
in the immediate vicinity of the leaves is produced, and 
motion immediately takes place. 
We will not occupy ourselves with an explanation of the 
cause of the descent of the sap : gravitation will serve the 
purpose, in the room of a more plausible conjecture. 
But, notwithstanding all the differences which exist 
among trees, they approach each other by insensible de- 
grees; and yet they individually retain a peculiar set of 
characters, and a physiognomy, which botanists call habit, 
that renders it easy to distinguish them at great distances; 
and more easy to eyes habituated to the sight of them, by 
practice and long familiarity, than by the aid of theory. 
Buff on’s Nat. Hist. 
CARBONATED SPRINGS. 
Carbonic acid gas is very plentifully disengaged from 
springs in almost all countries, but particularly near active 
or extinct volcanos. This elastic fluid has the property of 
decomposing many of the hardest rocks with which it 
comes in contact, particularly that numerous class in whose 
composition felspar is an ingredient. It renders the oxide 
of iron soluble in water, and contributes, as was before 
stated, to the solution of calcareous matter. In volcanic 
districts, these gaseous emanations are not confined to 
springs, but rise up in the state of pure gas from the soil in 
various places. The Grotto delle Cane, near Naples, af- 
fords an example, and prodigious quantities are now annu- 
ally disengaged from every part of the Limagne d’ Auvergne, 
where it appears to have been developed in equal quantity 
from time immemorial. As the acid is invisible, it is not 
observed, except an excavation be made, wherein it imme- 
diately accumulates so that it will extinguish a candle. 
There are some springs in this district, where the water is 
seen bubbling and boiling up with much noise, in conse- 
quence of the abundant disengagement of this gas. The 
whole vegetation is affected, and many trees, such as the 
walnut, flourish more luxuriantly than they would other- 
wise do in the same soil and climate, — the leaves probably 
absorbing carbonic acid. This gas is found in springs rising 
through the granite near Clermont, as well as in the ter- 
tiary limestones of the Limagne. In the environs of Pont- 
Gibaud, not far from Clermont, a rock belonging to the 
gneiss formation, in which lead-mines are worked, has 
been found to be quite saturated with carbonic acid gas, 
which is constantly disengaged. The carbonates of iron, 
lime, and manganese are so dissolved, that the rock is ren- 
dered soft, and the quartz alone remains unattacked. Not 
far off is the small volcanic cone of Chaluzet, which once 
broke up through the gneiss, and sent forth a lava stream. 
The disintegration of granite is a striking feature of large 
districts in Auvergne, especially in the neighbourhood of 
Clermont. This decay was called, by Dolomieu, “la ma- 
ladie du granite;” and the rock may with propriety be said 
to have the rot , for it crumbles to pieces in the hand. The 
phenomenon may, without doubt, be ascribed to the conti- 
nual disengagement of carbonic acid gas from numerous 
fissures. In the plains of the Po, between Verona and 
Parma, especially at Villa Franca, south of Mantua, I ob- 
served great beds of alluvium, consisting chiefly of primary 
pebbles percolated by spring water, charged with carbonate 
of lime and carbonic acid in great abundance. They are, 
for the most part, encrusted with calc-sinter; and the 
rounded blocks of gneiss, which have all the appearance of 
solidity, have been so disintegrated by the carbonic acid as 
readily to fall to pieces. The Po and other rivers, in wind- 
ing through this plain, might now remove with ease those 
masses which, at a more remote period, the stream was 
unable to carry farther towards the sea; and in this exam- 
ple we may perceive how necessary it is, in reasoning on 
