plant feeds. We ourselves are perpetually dissipating our
substance in our acts of life and work into the carbonic acid, water,
ammonia, and minerals on which plants feed. We "die daily" in as true
a sense as that in which the apostle used the term. And out of the
debris of the animal frame the green plant builds up leaf and flower,
stein and branch, and all the other tokens of its beauty and its life.

If, then, an animal can only live upon living matter--that is to say
on the bodies of other animals or of plants--with water, minerals and
oxygen gas from the air thrown in to boot, we might be tempted to hold
that in such distinctive ways and works we had at last found a means
of separating animals from plants. Unfortunately, this view may be
legitimately disputed and rendered null and void, on two grounds.
First of all, the mushrooms and their friends and neighbors, all true
plants, do not feed as do the green tribes. And secondly, many of the
green plants themselves can be shown to have taken very kindly to an
animal mode of diet.

A mushroom, thus, because it has no green color, lives upon water,
oxygen, minerals, and organic matter. You can only grow mushrooms
where there is plenty of animal matter in a state of decay, and as for
the oxygen, they habitually inhale that gas as if they were animals.
Non-green plants thus want a most characteristic action of their green
neighbors. For the latter in daylight take in the carbonic acid gas,
which is composed of carbon and oxygen. Under the combined influence
of the green color and the light, they split up the gas into its two
elements, retaining the carbon for food and allowing the oxygen to
escape to the atmosphere. Alas! however, in the dark our green plant
becomes essentially like an animal as regards its gas food, for then
it is an absorber of oxygen, while it gives off carbonic acid. If to
take in carbonic acid and to give out oxygen be held to be a feature
characteristic of a plant, it is one, as has been well said, which
disappears with the daylight in green plants, and which is not
witnessed at all in plants that have no green color.

So far, we have seen that not even the food of plants and animals can
separate the one kingdom of life from the other. The mushroom bars the
way and the green plant's curious behavior by night and by day
respectively, in the matter of its gas food, once more assimilates
animal life and plant life in a remarkable manner. Still more