THE ORGANIC REALM 573 



imposed by the conditions under which they hve; 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 Linnsean 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 zool- 

 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, 



