Mr. Worsley-Benison has been discussing this question in a very
interesting way, and he says in conclusion that "_physiologically_ the
most distinctive feature of plant-life is the power to manufacture
protein from less complex bodies; that of animal-life, the absence of
such power." He finds that in form, in the presence of starch, of
chlorophyl, in power of locomotion, in the presence of circulatory
organs, of the body called nitrogen, in the functions of respiration
and sensation, there are no diagnostic characters. He finds, however,
"fairly constant and well-marked distinctions" in the presence of a
cellulose coat in the plant-cell, in digestion followed by absorption,
and in the power to manufacture protein.
The _morphological_ feature of plants is this cellulose coat; of
animals, its absence; the _physiological_ peculiarity of plants, this
_manufacturing power_; of animals, the want of it. But after all the
discussion he says: "To the question, _Is this an animal or a plant?_
we must often reply, _We do not know_."--_The Microscope._
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