222 COMPARATIVE ZOOLOGY 



pair are approximately equal. But in both all work 

 done is paid for by waste of substance already formed. 



In combining carbon dioxide and water to form starch 

 the plant sets oxygen free (6(CO 2 ) + 5(H 2 O) = C 6 H 10 O 5 

 + 6(O 2 )) : in oxidizing starch or other food the animal 

 uses oxygen and sets carbon dioxide free. The green 

 plant in the sunlight, then, gives off oxygen and uses 

 carbon dioxide, while plants, which have no chlorophyl, 

 at all times, and all plants in the darkness, use oxygen 

 and give off carbon dioxide, like an animal. Every 

 plant begins life like an animal a consumer, not a 

 producer : not till the young shoot rises above the soil, 

 and unfolds itself to the light of the sun, at the touch 

 of whose mystic rays chlorophyl is developed, does real, 

 constructive vegetation begin ; then its mode of life is, 

 in a sense, reversed; since more carbon is combined 

 than liberated, and more oxygen set free than main- 

 tained. 



Most plants, and many animals, multiply by budding 

 and division ; on both we practice grafting ; in both the 

 cycle of life comes round again to the ovule or ovum. 

 Do annuals flower but to die ? Insects lay their eggs 

 in their old age. 



Both animals and plants have sensibility. This is one 

 of the fundamental physiological properties of proto- 

 plasm. But in plants the protoplasm is scattered and 

 buried in rigid structures : feeling is, therefore, dull. 

 In animals irritability is a highly developed property of 

 certain organs, and so feeling, like electricity rammed 

 into Ley den jars, goes off with a flash. 65 Plants prob- 

 ably never possess consciousness or volition, as the 

 higher animals do. 



The self-motion of animals and the rooted state of 

 plants is a very general distinction ; but it fails where 

 we need it most. It is a characteristic of living things 



