270 
MOTIONS IN PLANTS. 
the effect of each change of the thermometer on it, and how 
breathing on it even at a distance lifts it up, nay, convulses it, 
' nearly ten minutes after one should suppose any immediate 
effect must be passed if then the spiral wire can be taken out 
of the plant, and in this situation exhibit all the motions of the 
leaf} and that the refuse remaining after this dilapidation is 
perfectly inert ; surely I may say that the spiral is the cause of 
the motion ; and if this same wire is affected, in a superior 
Answers to Ik- degree, and answers to all the variations nf the barometer and 
variation of 
tl)e barometer tliermometer, so as to be visibly affected at the same time, and, 
ami iheniio- indeed, so much mere sensibly than either as to contract and 
meter. ' , ^ 
dilate when no changes in those instruments are produced, but 
to be affected highly when any alteration of either takes place ; 
may I not then be allowed to say that the spiral is governed by 
light and moisture, and is the cause of motion in plants ? Heat 
and light, I believe, never appear witliout causing a great increase 
of moisture in the air, for I never could augment the light 
greatly on the solar microscope, without producing a steam on 
the glass. I shall not add the mechanism of more sepile leaves 
lest I tire my readers ; but before I close the subject of leaves, 
I must notice that their mechanism is not in any thing more 
marked than their manner of decaying : the effect of the cold 
on the gatherers ; the distortion of the leaves in those parts 
marked by the muscles, are so many proofs of their being the 
cause of the contraction. Bui no sooner do the hairs disap- 
pear, and the oil with them, than the very rigidity the frost 
brings, renders the spirals more liable to break, they crack with 
the first wind, and the leaves fall to the ground : but before they 
fall they shew (though still on the tree) that something is 
wanting to them, that they once possessed •, they can neither 
turn, nor lift themselves up, but hang a dead weight, unable 
to screen their back from the sun’s rays, or protect their face 
from the piercing wind, but falling on each other, increase the 
decay by the general contact. And this is caused by the 
breaking of the spiral wire, the natural consequence of its 
rigidity : I shall now turn to the mechanism discovered in the 
flowers. - 
Ilcchnuical 
force shewn 
in decaying. 
There 
