PHILOSOPHY OF ZCOLOGY. 
foes 
i9 
touches the inner part of each filament, near the bottom. 
The irritability of that part is such, that the filament imme- 
diately contracts there, and consequently strikes its anther, 
full of pollen, against the stigma. Any other part of the 
filament may be touched without this effect, provided no 
concussion be given to the whole. After a while, the fila- 
ment retires gradually, and may again be stimulated ; and 
when each petal, with its annexed filament, is fallen to the 
ground, the latter, on being touched, shews as much sen- 
sibility as ever *.” 
In another British plant, the Cistus helianthemum, which 
is very common on dry rocky ground, the filaments, when 
touched, execute a motion the reverse of that of the Bar- 
berry. They retire from the style, and lie down in a 
spreading form upon the petals. This curious example of 
vegetable irritability was first pomted out by Dr Hoprx, 
Professor of Chemistry at Edinburgh +. 
In animals, this power is displayed by all muscles, m 
different degrees of intensity, producing directly, the va- 
rious Involuntary motions; and indirectly, those which are 
termed Voluntary. In the former of these, an action takes 
place upon the application of a stimulus, mdependent of 
the will; while, in the latter, the action takes place in the 
muscle, in consequence of volition exercised through the 
medium of the nerves. When the nerve of a muscle is 
cut across, and direct communication with the brain thus 
interrupted, the will ceases to exercise its controul over the 
motions of the fibres; but involuntary motion, or the pe- 
culiar irritability of the muscle, continues in force. 
By zoologists in general, the muscular fibre is regarded 
as deriving this power from nervous energy; since, as they 
* Smitn’s Introduction to Botany, p. 325 
+ English Botany, vol. xix. No. 1321, 
