compared with the oxygen thrown out during the day. When they are
flowering, plants exhale carbonic acid in considerable quantity, and at
the same time evolve heat. In this condition, therefore, they resemble
animals as regards their relation to the air; and a number of plants
placed in a room would, under these circumstances, tend to vitiate the
air.

"While the phanerogamia, or flowering plants, depend on the air almost
entirely for their supply of carbon, and are busy during the day in
restoring to it the oxygen that has been removed by animals, many of the
inferior cryptogamia, as the fungi and parasitic plants, obtain their
nourishment from material that has already been organized. They do not
absorb carbonic acid, but, on the contrary, they act like animals,
absorbing oxygen and exhaling carbonic acid at all times. It is,
therefore, evident that their presence in a room cannot be productive of
good results.

"Aside from the highly deleterious action that plants may exert on the
atmosphere of a sleeping room, by increasing the proportion of carbonic
acid during the night, there is another and more important objection to
be urged against their presence in such apartments. Like animals, they
exhale peculiar volatile organic principles, which in many instances
render the air unfit for the purposes of respiration. Even in the days
of Andronicus this fact was recognized, for he says, in speaking of
Arabia Felix, that 'by reason of myrrh, frankincense, and hot spices
there growing, the air was so obnoxious to their brains, that the
very inhabitants at some times cannot avoid its influence.' What the
influence on the brains of the inhabitants may have been does not at
present interest us: we have only quoted the statement to show that long
ago the emanations from plants were regarded as having an influence on