alleged to take place in Plants. 245 
a glass when a vegetable is placed there, is the chief question : 
Does it really proceed from the plant ? 
To ascertain this fact, and to prove the truth beyond all con- 
tradiction, has been the work of years of my life : to try the cause, 
I placed a stone instead of a plant, and the effect was nearly 
the same; a moist sponge was also inserted; but there is a still 
more convincing trial. A friend of mine has a large skylight, 
and he was lamenting the necessity of putting a glass within and 
a trough for carrying off the water which flowed; though no 
aperture was discoverable, still the stairs were inundated; they 
could not perspire ; the water therefore must have proceeded from 
the condensation of the atmosphere without, as it does in an 
empty room when the water is often perceived running down the 
glass window though no one is within: still resolved not to fail 
for want of experiment, I tried what appeared to me an unanswer- 
able one. I placed two plants in separate glasses of the same 
size: I covered one with a large cylinder; the other remained 
uncovered, except by the first glass: that which had two glasses 
has water (as in the skylight) running down the interior of the 
outward cylinder; no moisture, or a most trifling quantity, wil! be 
discovered where the plant is, as, when coilected, it at no time 
gave two drops, the mere evaporation of the vegetable; but the 
other ran down a large quantity at the interior of the cylinder 
as usual. I know not how I can add more convincing experi- 
ments; the last I have tried repeatedly. 
There can be no doubt, I should suppose, that the difference 
of ealoric within aud without the cylinder should cause some dif- 
ference in moisture. The earth which evaporates so violently 
must greatly increase the water discovered within the frames of 
the Cucumber and Melons. But all this, if duly considered, and 
the great discoveries of Priestley and Ingenhousz, since Hales 
wrote, must cause new ideas, new conclusions: I merely lay my 
crude notions before the public, and submit them to more learned 
jadges. But I cannot help adding, that had our trees perspired 
as botanists inform us they do, our trees, instead of the beautiful 
figure they make, would have appeared a mass of filth. 
Bonnet (the most exact French botanist that country pos- 
sessed) says he is persuaded that the leaves are garnished with 
orgaus for absorbing nutriment, which pass from them into the 
leaf: but unfortunately, instead of seeking with a microscope 
for those hairs or instruments which Nature has bestowed on the 
leaves, he sought them only by other experiments, microscopes 
being then not used on botanical occasions, or not good enough 
_ to satisfy him. Du Hamel expresses himself as perfectly con- 
vinced that absorbing organs of the leaf exist, though his micro- 
scopes are too feeble to enable him to judge of them iia 
. ut, 
