26 
THE FLORIST’S JOURNAL. 
night they vitiate the air by robbing it of its oxygen ; by day 
they purify it, by restoring to it a new supply. It is an interest¬ 
ing question, whether or not this alternation leaves the atmos¬ 
phere nearly in a state of equilibrium, or whether the proportion 
of oxygen becomes gradually increased; that it does so is a pre¬ 
vailing opinion : in primaeval ages it is conjectured that carbonic 
acid was present in excess, and that the action of vegetation has 
wrought the change we now perceive; and if this be true, we 
can scarcely doubt but that the same causes and influences are 
in constant operation. When we consider the great loss of 
oxygen which is caused by the respiration of animals, and by its 
combination with various mineral matters, it would seem almost 
incredible but that the air should in time become so far deprived 
of oxygen as to be unfit for the maintenance of animal life, were 
w r e not to look for some ceaseless compensating action; and by 
various experiments which have been made, it appears evident 
that the power of thus acting does reside in the vegetable 
kingdom. 
Taking this view, plants may be regarded as a special provi¬ 
sion of Creative Wisdom, by whose means the consumption of 
that which would render the world uninhabitable to man 
and the inferior creatures is secured: and at the same time we 
may perceive that they have been so beautifully contrived, that 
their existence could not be maintained, except by their con¬ 
tinually abstracting from the atmosphere those elements which, 
if permitted to accumulate, would endanger, if not totally prevent 
our own. 
Some leaves possess the property of moving when acted on by 
certain bodies, and this is termed irritability: it may be re¬ 
garded as being particularly the result of vital action, and is 
illustrated by the circumstance, that when a vine-leaf is sus¬ 
pended from a string it turns towards the light just as when on 
the plant. The Mimosa sensitiva folds up its leaves when 
touched. The movements in the leaves of Dioncea muscipula, 
and of the species of Drosera ; in the capsular valves of Impa- 
tiens ; in the column of Stylidium; in the anthers of Kalmia, 
and of the common barberry; and in the stigma of Mimulus, 
are some among the numerous recorded instances in which the 
irritability of different organs is evinced by the touch. Solar 
light, together with the atmosphere, also possesses great influence 
on the leaves of plants and their modifications, tending to induce 
