939 PRINCIPLES OF BOTANY, ETC. 
sensitiva, ¢asta, ot Oxalis sensitiva, Dionaea musci- 
pula, and other plants which grow within the tropics 
and under the Equator only, contract when touched. 
Less conspicuous, but easily demonstrable, is the 
contractility in the indigenous species of sun-dew, 
Drosera rotundifolia and longifolia. Vhe filaments of 
Urtica, Parietaria, Berberis and others show great 
irritability, and likewise the pistils of some plants, 
especially the stigma of Martynia. Light acts asa 
particular stimulus upon plants as experiments have. 
shewn. 
Gautier and Brandis think the parenchyma endowed 
with irritability, which in animals, after they died of 
painful convulsions, they found so strait as when cut 
to emit a creaking sound. Rafn speaks of having 
found the parenchyma of the species of Euphorbia, 
in which he made frequent incisions, in a very tense 
state : he does not, however, attempt to decide, whe- 
ther the parenchyma is the only substance which 
possesses irritability. He assumes a muscular fibre, 
(§ 233), in plants, and contends with Abilgaard, that 
in all probability the seat of irritability is the pa- 
renchyma, and that muscles are its conductors. 
Sensation, which in the animal 1s produced only 
by the nerves, has not hitherto been met with in 
the vegetable kingdom, nor have nerves yet been 
found in plants. It does not however follow, that 
they are destitute of nerves. But it certainly would 
be a precipitate conclusion, were we, with Dr Per- 
cival, from some not sufficiently demonstrated facts, 
to conclude as infallibly true, that plants have sen- 
sation or consciousness. We can go as far only, as 
A our 
