20 
PLANTS. 
its welfare, and if there is a chink in the apartment 
which admits the light, it will grow towards it. If 
the plant be afterwards removed into the open air, 
it will soon lose its sickly appearance, recover, at 
least in a degree, its strength, and assume its natural 
colour. The knowledge of this fact has suggested 
to us the means of improving several of our succu- 
lent vegetables ; and yet there are many gardeners 
who earth up their celery, and tie up their lettuces; 
and many persons who consume both, without be- 
ing at all aware how this change is really effected. 
Irritability of the Organs of Plants. 
This is a curious and interesting part of the vege- 
table ceconomy ; it occurs in many instances, and 
the motion produced is always the same in each in- 
dividual, however frequently it may be repeated. 
A considerable number of plants are more or less 
irritable, according to their age, their strength, or 
the part which is touched. This is not only visible 
in their leaves, but extends to the flowers, and the 
different parts of fructification. Among other au- 
thors who have noticed this very curious property, 
we must not neglect to mention M. Duhamel, who 
has admirably described the motion of the sensitive 
plant. Bonnet, likewise, in his Reclierclies sur 
V usage des Feuilles, has observed that, in their mo- 
tions, they always present their surface to the open 
air, and that whenever the branches of the shrub 
are displaced the leaves constantly take a new 
