Payee, 
706 
Octob. where there was lefs Light, ‘The Lobes were 
eee raifed in the Morning; but not to a horizontal 
Situation : and they drooped earlier at Evening. | 
The third Day it was fet in a South Window, 
open to the full Sun. Early in the Morning the 
Leaves had attained their horizontal Situation; 
by nine o’Clock they were raifed confiderably; 
and they continued in this State till toward 
Evening, when they by Degrees fell to the 
_ horizontal Situation; and from that drooped 
gradually to the ufual State of. Reft. 
The fourth Day the Plant ftood in the fame | 
Place, but the Sun did not appear. The Lobes 
obtained early their horizontal Situation, but 
did not rife beyond it; and in the Evening 
they clofed as ufually, below. 
“Thefe Experiments fhew the Effects of various 
Degrees of Light; at the fame Time, that 
they prove the whole Change to be occafioned 
by Light only. 
The Effect of moderate Light, that is, the 
Light of a bright Day out of the Sun-fhine, 
is to raife the Lobes to an horizontal Po- 
fition: lefs than this places them at an obtufe 
Angle downward: more at an obtufe Angle 
upwards. 
The fifth Day the Plant was fet in a lefs 
enlightened Room: and the Leaves had ob- | 
tained by nine o’Clock their Pofition' at an obtufe 
Angle downward: it was then brought into the 
lighter Room, and they rofe to the horizontal 
Situation in a Quarter of an Hour. It was after 
this removed tothe Window, where the Sun fhone, 
and the Lobes were elevated as before: and 
being thence carried into the lefs light Room, 
they drooped again. All thefe Changes were 
produced between the Hours of nine and two; 
the Weather being the fame, and only the Place 
of the Plant changed. . . 
On the fixth Day it remained in moderate 
Light; and kept its Leaves horizontal. 
On the feventh I made the final Experi- 
“ment. 
_ ‘It appeared to me that. if Licht were the 
fole Caufe of the Motion, and Change of Po- 
fition in the Leaves, then denying the Plant the 
Benefit of Light at any Time, mutt bring on that 
Change: that it would not be difficult to darken 
the Place where the Plant ftood, at any Time: 
and that the Confequence of this muft be, if the 
Principles already laid down were true, a bringing 
on of the Change at any Time of the Day. This 
Experiment appeared as a juft Proof of the fore- 
going Reafonings. If Darknefs would at any 
Time throw. down the Lobes, the Syftem of 
that Motion before delivered muft be true; if | 
not, all the Reafonings muft be falfe. 
~The Affent of the World muft alfo depend | 
on this: Deductions of Reafon may be dif- 
puted, but it will be allowed certainly, that 
we underftand the Caufe of. a Change which 
we can produce. 
In the Evening of the fixth Day I fet the 
Plant in a Book-cafe, on which the Morning- 
I 
A GOMPEHAT BODY 
~- Dotcom 
Sun fhines; and throwing open the Doors, left O&ob. 
the whole to Nature. The fucceeding Day waa | 
bright. The Lobes which’ had met in their 
drooping Pofition at Evening, and continued fo 
during the Night: began to open early in the 
Morning; and by Nine o’Clock they had pafled 
their horizontal Situation, and were elevated in 
the ufual Manner. | | 
I then fhut the Doors of the Bookcafe: the 
Plant was by this left in Darknefs ; and on open- 
ing them an Hour afterwards, the full Change 
had happened ; the Lobes were all drop’d, and 
it was in the fame State that it would have 
fhewn at Midnight. 
our own Time, put on all its Changes, from the 
drooping to the moft elevated Pofition of the 
Lobes. : , 
We know that in thefe Experiments, Light 
alone is the Caufe: we are therefore certain, 
that what is called the Sleep of Plants, is the 
Effect of the Abfence of Light alone, and that 
their various intermediate States are OWINS to its 
different Degrees. 7 | 
This being explained, a fecond Difcovery fol- 
lows naturally. The Motion of the fenfitive 
Plant, at the Caufe of which no Philofopher has 
hitherto ventured a ConjeCure, is in a great mea- 
fure owing to the fame Principles: and the Fx- 
planation of it, which before the Effeé of Light 
upon the Leaves of Plants was thus fhewn, muft 
have been enveloped in impenetrable Ob{curity, 
may now be regularly purfued. . 
The fenfitive Plant, befide its finoular uality 
of clofing, and dropping its Leaves upon the 
Touch, is fubject to the fame Changes with the 
Abrus, and thofe’ other Kinds, we have named 
from the Effect of Light. 
are about twelve 
‘ir ta in an horizontal] 
Direction. : 
Thus the young Plant appears in the middle 
Hours of Day. At the Approach of Evening, 
the 
