MOTIONS fN PLANTS. 
267 
long been labouring to shew : viz, that the spiral wire is the 
cause of all motion in plants ; and that there is no such thing as 
perspiration in plants. 
That the regular motion in plants is little, or not at all Motiou of 
, . , ... . , iilants little 
known, is but too true, for to examine it, requires a degree of ^nown. 
attention few will give, and a constant watching of plants that 
scarcely any will bestow; but the most regular instrument is 
not more exact in its daily motion than the leaves of most trees, 
especially those which have long i>eduncles : the necessities of 
each leaf arc a certain portion of light without which it decays : 
there is not any thing (darkness excepted) which so soon destroys 
it, as being in too close contact with other leaves ; nature has, 
hereforc, bestowed two gatherers for the regulation of its mo- 
tion, one adjoining the stem, the other the leaf, and at the ter- 
Tiination of each gatherer, is pl.iced a ball on w hich the jiedun- 
:le or leaf turns as on a pivot, which carries each nearly two 
birds of a circle by means of the elongation and contraction of 
he spinal wire. But they do not move alike: the gatherer ^lotion of tlir 
lext the leaf moves perpendicularly, andean, therefore, raise 
ir depress the leaf to prevent its reposing on others, or injuring 
hose beneath it by usurping too much light : while the gatherer 
idjoining the stem, whose motion is horizontal, can follow the Horiznnti*l 
laily course of the sun ; or by spreading to one side or the 
ither, adapt itself to catch those gleams of light that pass 
KJtween the different leaves and offer a fa\oarable situation : 
nd such is the admirable delicacy of the spiral wire, that each 
Iteration of light, though ever so trifl'ng, produces a new effect 
n the tender mechanism which governs the whole, and renders 
i capable of moving to that situation best fitted for it. But it 
) not the gatherer of the leaf .alone which governs the mul-rib 
nd side rib: each of these spires h.ive a bail which forms their 
entral point ; in which the muscles meet, and to which they 
II adhere, either to make the leaf flat and straight, or to draw 
into a concave or convex form, as the situation of the .atmos- Concave or 
here pro|>els. com ex, notion 
It must be observed also that there are only two moments in 
1 C existence of a leaf in which it can turn its back to the sun : 
U 2 when 
