PLANTS AND ANIMALS DISTINGUISHED. 25 



pendent for their food on the compounds put together in 

 plants. Colorless plants, as Fungi, possessing no chloro- 

 phjl, feed, like animals, on organic compounds. No living 

 being is able to combine the simple elements carbon, ox- 

 ygen, hydrogen, and nitrogen into organic compounds. 



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

 monia) or liquid (water containing substances in solution), 

 that of animals usually more or less solid, though solid 

 substances must be changed to liquids before being capable 

 of absorption into the tissues. The plant, then, absorbs 

 these foods through its outer surface, while the animal 

 takes its nourishment in larger or smaller masses, and di- 

 gests it in a special cavity. A few exceptions, however, 

 occur on both sides. Certain moulds seem to swallow 

 their food, 7 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 energy 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 a ) + 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 



