PLANTS AND ANIMALS DISTINGUISHED. 25 



pendent for their food on the compounds put together in 

 plants. Colorless plants, possessing no chlorophyl, feed, 

 like animals, on organic compounds. No living being is 

 able to combine the simple elements carbon, oxygen, hy- 

 drogen, and nitrogen into organic compounds. 



The food of plants is gaseous (carbon dioxide and am- 

 monia) or liquid (water), that of animals usually more or 

 less solid. The plant, then, absorbs these foods through 

 its outer surface, while the animal takes its nourishment 

 in larger or smaller masses, and digests it in a special cav- 

 ity. A few exceptions, however, occur on both sides. 

 Certain moulds seem to swallow their food, and certain 

 animals, as the tape-worm, have no digestive tract. 



Plants are ordinarily fixed, their food is brought to 

 them, and a large share of their work, the formation of 

 organic compounds, is done by the force of the sunlight; 

 while animals are usually locomotive, must seek their 

 food, and are unable to utilize the general forces of nature 

 as the plant does. The plant is thus able to grow much 

 more than the animal, as very little of the nourishment 

 received is used to repair waste, while in most animals the 

 time soon comes when waste and repair 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 diox- 

 ide, 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 chlo- 



