450 On the upright Growth of Vegetables. (Jone, 
one or other, or both, of these modes, we may expect to find the 
buoyant principle operating in the upright growth of vegetables, 
It is apparent that vegetables might be so constructed as, by an 
extrication of the lighter gases contained in the sap, to create a 
buoyancy, which, by pressing to the top of the plant, would tend 
to expand it in a perpendicular direction. Water, which serves so 
many purposes in vegetation, contains one of those ingredients 
which form carbonic acid; and the formation of carbonic acid, 
according to some of our best naturalists, is the great business of 
vegetable life. Such a decomposition of water must disengage the 
hydrogen, the greater part of which, however, seems to re-enter 
into immediate combination, Were that gas found in a free state, 
we could have no difficulty in ascribing to its agency the upright 
growth of plants. I have not learned that any.experiments have 
been made to ascertain the existence of free hycrogen gas in plants, 
but I conclude that there cannot be any great quantity, otherwise 
it would have been incidentally noticed by those who were engaged 
in the decomposition of vegetable substances with other views. 
Having no proper apparatus, and being but an awkward experi- 
menter, I cannot rely on the result of a slight attempt made by 
myself. Having raised a few garden beans when the stems reached 
the length of eight or ten inches, I cut them into three divisions ; 
and squeezing the highest, middle, and lowest, parts of the germen 
under three glasses, placed. in a chemical bath, I collected the gas 
from these parts. A small quantity was collected from the tops and- 
middle parts; but as the only test I tried was to expose it toa 
‘flame, I could only conclude in general that it did not contain much 
hydrogen, because there appeared no inflammability. From these 
circumstances, however, and the important fact that there is another 
buoyant gas which certainly does exist in plants, we cannot with 
any probability ascribe the chief agency to the buoyancy of 
hydrogen. 
It was for some time a favourite idea with me that the sap itself 
at different altitudes was of different densities; and thence, from 
the law of relative attraction, that it produced an upward pressure, 
The expression itself, too, (ascent of the sap) apparently carried in 
its own terms the solution of the question ; for whatever might be 
the cause of the ascent of the sap, that ascent seemed to be a very 
good reason why the tubes in which it flowed did ascend, 1 am now 
satisfied that these notions were founded on erroneous views, they 
being inconsistent with the facts ascertained by experiment. 
The luminous, yet condensed, view of the opinions relative to 
the ascent of the sap in vegetables, given by Dr. Thomson in his 
System of Chemistry, nearly demonstrates that the ascent of the 
sap is not affected by gravitation; and as experiment has proved 
that the sap itself becomes heavier as it ascends, it is evident that no 
buoyancy can be ascribed to it. The sap of vegetables seems to be 
analogous to the blood of animals, and the ascent of the sap, by 
which the nourishment is administered to the plant, may be paral- 
