CHAPTER XI 



THE DIFFERENCES BETWEEN ANIMALS AND PLANTS: 

 THE MUTUAL RELATIONS OF ORGANISMS 



THE DIFFERENCES BETWEEN ANIMALS AND PLANTS 



IF we confine our attention to the larger organisms, the 

 differences between plants and animals are very evident; but 

 when we turn our attention to some of the lower members of 

 each group, the differences are less evident and most of them 

 disappear. A castor bean and a frog are very unlike, but 

 Peranema and Euglena (Fig. 29) are so similar that it is 

 hardly possible to say whether either of them is an animal 

 or a plant. 



In their life functions, too, the higher plants and animals 

 differ widely. Most of the general functions of animal life 

 are possessed in a modified form by plants also; but since 

 some functions are possessed by animals alone, a division of 

 functions into two categories is frequently adopted. 



Vegetative functions are those possessed by both animals 

 and plants. They are chiefly associated with food and growth, 

 and are: alimentation, circulation, respiration, excretion, and 

 reproduction. 



Animal functions are those possessed by animals and not 

 by plants. They are motion and coordination. 



Both animals and plants have vegetative functions, but they 

 are carried on quite differently in the two groups, resulting in 

 a radically different type of life in animals and plants. The 

 study already made of the biology of organisms enables 

 us now to ask intelligently, What is the difference be- 

 tween animals and plants? Although it is fairly easy to see 

 the difference between a tree and a dog, when we come to 

 extend the comparison to smaller and lower organisms it 

 becomes more and more difficult to determine any distinc- 



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