Chlorophyl is
the green coloring matter of plants, and is, of course, a typical
product of the vegetable world; yet it is made by such animals as the
hydra of the brooks and ponds, and by many animalcules and some worms.
Starch is surely a typical plant product, yet it is undoubtedly
manufactured, or at least stored up, by animals--a work illustrated by
the liver of man himself, which occasionally produces sugar out of its
starch.
Again, there is a substance called _cellulose_, found well nigh
universally in plants. Of this substance, which is akin to starch, the
walls or envelopes of the cells of plant tissues are composed. Yet we
find those curious animals, the sea squirts, found on rocks and stones
at low-water mark, manufacturing cellulose to form part and parcel of
the outer covering of their sac-like bodies. Here it is as if the
animal, like a dishonest manufacturer, had infringed the patent rights
of the plant. On the fourth count, then--that of chemical
composition--the verdict is that nothing that chemistry can teach us
may serve definitely, clearly, and exactly to set a boundary line or
to erect a partition wall between the two worlds of life. There yet
remains for us to consider a fifth head--that of the food.
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