‘OF GARDENING 
Octob. the Lobes begin to draw themfelves together up- 
—————_ wards, as in the Parkinfonia; and the middle 
Rib of each approaches toward the other: at 
Night the Lobes are as entirely {hut upwards, 
as thofe of the Abrus downwards: the two Ribs 
are placed clofe to each other, and the Footftalk 
which fupports them both, hangs down. | 
This is the State of Repofe of the fenfitive 
Plant: into this it falls every Night naturally ; 
and into this it may, in the fame Manner as the 
Abrus, be thrown at Noon Day in a darken’d 
Place. 
As we have feen the Caufe-of this Change in 
the Abrus, to be Light, and have traced the 
Manner of its Operation; it is eafy to follow it 
alfo in the fenfitive Plant, through the fame 
Courfe of Enquiry. 
At the Bafe of the Footftalk, where it joins 
the main Stem, there is a Clufter of complex Fi- 
bres: thefe have rifen from the medullary Part, 
and pierced the woody Sides of the Stem. 
From this complex Clufter, the Fibres pro- 
ceed in a ftrait Line up the Footftalk, till at 
the Head of that, where the two Leaves rife, 
there is another fuch Clufter: thence the Fibres 
run ftrait the Length of the main Ribs, and 
fend out on each Side other Clufters at the Bafe 
of every Lobe. From thefe the more minute Fi- 
bres run ftrait through the Leaf, and fend out 
lateral Shoots. . 
This the Microfcope difcovers plainly, and 
this fhews that not only the natural Motions of 
the fenfitive Plant, are the fame with thofe of 
the Abrus and others; but that the Conftruc- 
tion alfo is the fame in its Kind; though more 
complex. | 
In the Night the fenfitive Plant is not capa- 
ble of the common Motion on the Touch, for 
the Leaves are already in the Condition where- 
to they would be reduced by it. In the Day 
they rife and fpread: and *tis then the ftrange 
Effect appears on touching them. 
Light expands the Lobes, feparates the Ribs, 
and cailte the Footftalks. It does this, by put- 
ting all the Parts of them in a vibrating Motion. 
This we have feen in the Abrus, is principally 
effeéted by means of thofe Clufters of Fibres 
which are placed at the Bafes of the Footftalks, 
In this Plant, as there are no lefs than three 
Sets of thofe Clufters, the Effects of the fame 
Principle are naturally much greater than in the 
Abrus, where there is only one. 
The Vibration of the Parts is that which 
keeps the Leaves of the fenfitive Plant in. their 
expanded and elevated State: this is owing to 
a delicate Motion continued through every Fibre 
of them. ‘When we touch the Leaf, we give it 
another Motion more violent than the firft: this 
overcomes the firft: the Vibration is ftopped 
by the rude Shock; and the Leaves clofe, and | 
their F ootftalks fall, becaufe that vibrating Mo- 
tion is deftroyed, which = them elevated and 
expanded. 
That the Power of Motion’ in the fenfitive 
‘Plant depends upon the Effect of Light on the 
pee 
till they are expanded, they have no fuch Powet: 
The young Leaves, even when grown to half an 
Inch in Length, have no Motion on the Touch, 
though rough and fudden. 
To propagate the Motioh when the Leaves 
are in a State to fhew it, there requires a per- 
fect and confirmed State of thofe Clufters of Fi- 
bres lodged at their Bafe. This is evident: for 
when the young Leaf has firft come into the 
State of Vibration, a Touch will make its Lobes 
clofe; but the Effeét is not continued down the 
Footiftalk, till it is more confirmed. No fhock 
on the young Leaf will affeét the Footftalk be- 
fore it is expanded: hence the Clufters of Fibres 
at the Bafes of the Lobes firft acquire their due 
Condition for Motion, and afterwards thofe at 
the Head of the main Footftalk. 
As there requires a due Firmnefs to give the 
Clufters of Fibres this Sufceptibility of Motion, 
and Power of propagating it farther, there needs 
alfo a Concurrence of favouring Circumftances; 
to prefetve them iri that delicate State wherein 
they are capable of exerting thefe Powers: 
The cold Air hardens the Fibres, and impairs 
their Power of Motion. The fenfitive Plant 
becomes more languid in this Refpeét, when 
removed out of the Stove. _ 
‘The Correfpondence between this Motion, and 
what Linnaus has called the Sleep of Plants, 
or their natural clofing of their Leaves at 
Night, appears alfo in this Inftance: for as thé 
fenfitive by being removed out of the Stove, 
lofes in fome degree the Quality of clofing its 
Leaves on the Touch, the Tamarind by the 
fame Change lofes in great part its Quality of 
clofing the Leaves at Evening. This is proba: 
bly owing to the Juices ftagnating in the Clufters 
of Fibres; and to the Contraction of the Bark 
by. Cold. . 
The Communication of Motion is lefs from 
the Lobes to the Footftalk; and greater from 
the Footftalk to them: The greateft Shock is 
given to the Plant by a rude Touch of the 
Stem: but even this does not affeé the unexs — 
panded or young Leaves, | | | 
The Analogy between the Effect of a fudden 
Motion, and of the Abfence of : Light, is con= 
firmed alfo by this; for as Light decays natu- 
rally at Evening; of artificially by fhutting up 
the Plant, the Lobeas firft clofe, cenit the Foot= 
{talks dectwiatids fall. 
The Power of abfoluté Darknety t is greater on 
the fenfitive Plant, than that of the rudeft Touch. 
The rudeft Touch will only caufe the Lobes of 
the feparate Leaves to clofe, and the Footftalks 
to hang down: the two Leaves will remain far 
afunder. The Effeét of abfolute Darknefs ex- 
ceeds this; for the two Leaves clofe alfo abfo- 
lutely together, and it appears as if the Foot- 
{talk fupported only one: This proves that the 
Expanfion of thofe Parts depends folely upon 
the Effect of Light; and that although it may 
be difturbed by a fuperadled and ruder Mo- 
tion, 
oh 
expanded Surface of the Leaves, i8 certain, for Oétob: 
