138 SYSTEMATIC ZOOLOGY 



Plants really have their organs of feeding and of respi- 

 ration in their roots and leaves, while animals as high as 

 the parasitic worms have no special organs for taking food 

 or for respiration, the absorption of nourishment taking 

 place by the whole surface of the body. 



Several other tests have been suggested to separate 

 animals from plants. Plants reproduce by seeds, by 

 spores, and by buds; animals by means of eggs. Plants 

 take up carbon dioxide and give off oxygen; animals use 

 oxygen and give off carbon dioxide. Plants take either 

 liquid or gaseous nourishment, while animals partake of 

 solid food. Plants may have a peculiar green coloring 

 substance called chlorophyl, lacking in animals. Plants 

 produce a peculiar chemical substance known as cellulose. 

 These features when accurately analyzed are all seen to 

 have their exceptions. Many animals reproduce by bud- 

 ding, while the sexual reproduction of animals and of 

 plants is essentially the same. Plants require oxygen as 

 much as animals, and it is only the green plants which 

 give off oxygen; a mushroom or a toadstool takes up 

 oxygen and gives off carbon dioxide the same as does 

 any animal. Quite a number of animals possess chloro- 

 phyl, while it is lacking from many plants; and cellulose 

 is found even in the Tunicata. In the matter of food 

 the distinction is a little sharper. While some animals 

 like the parasitic worms take only nourishment in solution, 

 no plant takes solid nourishment. 



Yet, although we cannot frame a perfect definition which 

 will at once separate all animals from all plants, we prac- 

 tically have little difficulty in deciding any case that is 

 likely to arise in our every-day experience as to whether 

 the form in question shall be placed in the one kingdom 

 or in the other. 



