te eet, sone ieaienesieetaliiiieietie mentees taal ae reetemmtaeene neta ii 
Soft] of the Letéiuce, 
he observes, from a power inherent in the 
| plant itself, for it cannot be supposed that 
| the milky juice could be emitted through 
the organic pores of the lettuce, unless 
it had been propelled by a constrictive 
| power, or systolic motion in the vascu- 
| lar system; and as this power is excited 
_by the simple contact, or application of 
‘any body capable of producing excite- 
ment, aud ceases uniformly whea the 
‘stimulus i$ withdrawn, it must, on that 
account, be referred to a principle of irri- 
tability. 
This law, which is common to living 
matter, Dr, Carradorri conceives he has 
fully demonstrated to prevail in the let- 
zuce; since, as often as any solid body, 
whether rough or smooth, round or point- 
ed, was brought into contact with this 
plant when in flower, it never failed to ex- 
cite the part so touched to emit or eject 
amiulky fluid, in the same way as muscu- 
lar contractions are excited in animals, 
by the application of stimuli; this effect 
could not, however, be prolonged to an 
indefinite period by the continued appii- 
cation of the exciting body, though it was 
renewed, after a short interval, in the 
same manner as muscular contraction: 
cannot be extended beyond a certain pe- 
ried by the presence of the irritating 
cause, till after the lapse of some time, 
when the muscular fibre, having recovered 
its excitability, again becomes susceptible 
of excitement. 
Such an effect cannot, Dr. Carradorri 
goes on to observe, be referred to any 
mechanical cause, since he frequently 
found that the emission of moisture was 
not in proportion to the collision, or the 
pressure of tle body applied to a vegeta- 
ble, but to the excitement which it pro- 
duced; hence it is evident, that the phe- 
Nomenen in question is merely the effect 
of excitement or stimulation. Besides, 
he never perceived that a greater excite- 
ment was produced in the plant in_pro- 
portion to its being strongly rubbed, or 
even pricked by a very sharp body; on 
the contrary, it always appeared to be 
more considerable when the plant was 
only slightly rubbed by the finger, or 
gently touched by a blade of grass. 
Heat, cold, strong odours, volatile fluids, 
&c. are all, it is well known, capable of 
acting on the irritability of some vegeta- 
bles, as forexample, on the sensitive plant; 
but, according to Dr. Carradorri’s expert- 
meuts, they do not operate with suflicient 
power to excite the irritability of the let- 
tuce. Hence, it should seem, that the 
Maentury Mas., No, 162, 
copter Act 
re het. om 
and other Plants. £53 
irritability of this plant is not sensible to | 
every stimulus. 
After detailing these experiments, Dr, 
Carradorri makes the following pertinent, 
and judicious observation on the irritabie 
lity of plants in general, 
“The whole of my experiments (he 
observes) on the lettuce, as well as on 
diiferent species of plants*, incontestably 
prove that vegetables possess a princis_. 
ple similar to that which in animals is 
termed irritability, All vegetables ap- 
pear te possess this power, though in difa 
ferent degrees. On this principle des 
pends not only the absorbing power, and 
the ascent of sap in vegetables, but also 
the motion, or the circulation of the juices 
in their vessels. It is beyond a doubt, 
that fluids are absorbed and propelled by 
vegetables, so long as their vitality ree 
mains, and that, as soon as this principle 
is destroyed, the circulation immediately 
ceases. 
“ Senebier did not think that irritability 
was compatible with the rigid state of the 
lymphatic or succiferous vessels in vegeta- 
bles; and that from this condition, even 
were they endowed with that principle, it 
would be inavailable, as they could neither 
be susceptible of contraction nor dilata- 
tion. Hence he was led to maintain that 
the absorbing power of vegetables depends 
onan Hygroscopic or Thermometric action, 
similar to that of a sponge. According 
to this hypothesis, however, it can be of 
no consequence whether plants be fur- 
nished with an absorbent system of ves- 
sels, or be composed merely of a conge- 
ries of inorganic and impervious fibres. 
In fact, Senebier reduces vegetable life 
to a simple effect of physical causes. ; 
“« But how, upon his principle, can we 
admit any difference between a recent 
and a dry vevetable, or a living and a 
dead plant? How, besides, can we ex- 
plain the force with which the sap of 
plants is sometimes propelled to a con- 
* Numerous observations ptove that there 
are many vegetables endowed with more er 
less irritability in different parts. The sleep 
of plants and the vigils of flowers furnish a 
proof of this. Farther, irritability has been 
discovered in the generative organs of some 
plants, viz. in the stamens, the filaments, and 
the pistils. The observations and experi« 
ments of Gmelin, Smith, Covolo. Thoelven- 
ter, and Medicus leave no room to doubt of | 
There are besides many plants. 
this fact. 
which manifest this principle in the leaves 5 
as, for example, in the Hedysurum gyrans, Di- 
ea muscipula, the sensitive plant, &c. 
siderable 
CREE SE ee Lee 
Te A ele et meee Se ee, ee re 
