Otob. tion, yet it.can be taken’ away. abfolutely only 
«in the brighter Regions the Lobes are expand- 
soe. by Darknefs;. by. the. Defect ‘of that tO» which 
alone it was owing. | : y bovse anuoyed | 
 . Thefe Experiments every ne may eafily‘re- 
peat: the Obhfervations will be familiarly made by 
any who have Stoves: they are conftant and: in- 
variable, and. the Conclufions from them are cer- 
tain; for no other Caufe intervenes, 
The Effeét of Light is continual while the 
Light continues. The Plant therefore whofe | | 
Leaves have ‘been thrown down, and clofed by 
this rude Shock, is immediately affected by 
the Light, as at its firft’ Appearance in the 
Morning, or as on its. Admiffion, ‘when the 
Leaves had been‘ clofed by artificial Darknefs. 
The Vibration begins; and if the Light be at 
its full Strength, the Expanfion and Elevation 
of the Lobes is fo quick, that one may almoft 
look upon the Plant and fee it. A few Minutes 
often perfeéts it. 
That the Touch of the Leaves no other way 
affects them than by a Motion greater than their 
own internal Vibration, is plain from this, that 
-moft.raifed .of all, not .becaufe. it never rains; OGob, 
but becaufe theLight is conftante, 
its Leaves is proportioned always to the Degree 
of Light, and confequently it is affected by the 
cloudy or clear Weather, though the Plant’ re 
main in the fame Place. | 
The Lobes begin to rife before the Sun js a- 
bove the Horizon, - becaufe the Air is enlightened 
in a proportioned Degree; and they begin’ te 
clofe again long before it fets, becaufe in the 
South Window the Shadow of the Building 
‘darkens the Air about them. | 
In rainy Weather the Leaves wear the fame 
Appearance they would in a Plant native of a 
Country where there are Seafons of Rain; they 
never at any Time of the Day reach the horizon- 
tal Pofition, and they droop- much éearher in the - 
| Afternoon, and begin to expand much later in 
the Morning. 
The fenfitive Plant which in thefe Experiments 
was placed near the Abrus, was affected in the 
if they be touched with a Finger in fo delibe- | fame Manner: and by repeated and careful Exa- 
rate and gentle a@ manner as not to move them, | mination, I have always found, that in both 
no Effect is produced: and, on the other hand, 
it they be any other Way moved, the full Ef. 
’ fe follows. | 
thefe and in all others, the Degree of Elevation, 
or Expanfion in the Lobes, is exactly propor- 
tioned to the Quantity of Light; as it is folely 
If the Pot be foosks though no part of the | dependent on it. 
Plant be touched, the Leaves clofe, and their 
Footftalks fall: or if the Wind blow them, the 
 Effe& is the fame. | 
. Hence it is certain that the Expanfion of the 
Lobes, and Elevation of the Footftalks in thefe 
pinnated Plants, is occafioned folely by: that vi- 
brating Motion, in ‘which their Parts are kept 
by the continual Impulfes of Light: and con- 
fequently, that in. all of them they collapfe or 
fink on the Abfence of Light; and in the more 
delicate Kinds upon the Shock of any ruder | 
When the Yenfitive has been kept out of a 
Stove fome Days, and has loft fome part of its 
Power of Motion, if the Leaf be touched foftly, 
and the Force increafed gradually, it will bear 
a great deal without drawing up the Lobes; but 
at the fame Time a much lefs Preffure given with 
a fudden Stroke, will occafion their clofing. 
In this manner we may alfo trace the Extent 
and Progrefs of the Motion according to the 
Force; a flighter Shock raifing only the Lobes 
that are touched, a harder the oppofite ones, and 
Motion, which for the prefent {tops that Vibra- | { the whole. 
tion. ' 
Hence alfo the different Appearance of pin- 
nated Leaves in various Climates is underftood ; 
and may be affigned to its true Caufe, which is 
the different Degree of Light. 
ed, not becaufe of the Heat, but becaufe-the 
Light is ftrong: in the northern Kingdoms they 
droop, not from Cold, but. becaufe the Air is 
lefs enlightened: in the rainy Seafons they alfo 
droop, but it is not from the Moifture, but the 
Darknefs of the Weather; and in Egypt they are 
* 
This Quality in the Leaves of Plants, as their 
| general Structure is the fame, and the fame Agent 
Operates univerfally, ought to be found in all: 
though in various Degrees, according to the Con- 
| ftruction of their Parts. Ia this, as all the pre- 
ceding Inftances, juft Obfervation confirms the - 
Principles deduced from Reafon. In fome it is 
greater, in others lefs: in many obvious to the ° 
common Eye, in others difficultly perceived by 
the moft accurate ; but.on a ftrict and clo Exa-. 
mination, I have not found any Plant or Tree 
wholly unaffected by it. | $35 
E DE Ns 
The Abrus placed ina fouth window perfectly 
fhews this; for the Expanfion and Elevation of 
| 
