THE ORGANIC REALM 573 
imposed by the conditions under which they live; and in 
detaching certain portions of their substance, such as seeds 
or eggs, capable of developing from infancy to old age by 
taking in as food suitable materials, transforming them, then 
building them into their bodies, and finally after utilization, 
eliminating them as waste products. Such being the charac- — 
teristics of all living things we should hardly expect any well- 
marked peculiarities by which all animals can be distin- 
guished from all plants. In fact there is not a single point 
of difference available for separating sharply the animal from 
the vegetable kingdom. The Linnean criterion of feeling 
we have already found to fail when applied to primitive types. 
So also the popular criterion of motion or locomotion must 
be rejected by anyone acquainted with the lower forms of 
life, which include not only motile plants but fixed animals; 
and we have only to remember the absence of chlorophyll 
from many plants to realize that even this highly charac- 
teristic vegetable substance does not afford an adequate 
mark of distinction between the two kingdoms. Not a few 
organisms behave like plants at one stage, and like animals 
at another. A considerable number of these vegeto-animal 
organisms have been claimed alike by botanists and zodl- 
ogists. The uncertainty in classifying such forms has led 
to the suggestion that a third organic kingdom, intermediate 
between the animal and the vegetable, be recognized to 
include all the kinds in dispute. This suggestion has not 
met with much favor among naturalists, for instead of lessen- 
ing the practical difficulties of the case it would really double 
them by giving us two uncertain boundary lines instead of 
one. Our best way surely is to meet the difficulty by trying 
to.define as strictly as possible what may be conveniently 
meant by animal and plant, remembering that whatever 
definition we frame is sure to be arbitrary. 
We know that the great majority of plants organize in- 
organic material, while the great majority of animals, if 
not all, have no such power and so must depend upon plants 
for their food. The raw materials which plants build up into 
food have only to be absorbed in solution from the water, 
soil, or air in which they live. The elaborated food of animals, 
