FUNCTIONS OF PLANTS AND ANIMALS 



93 



are those which occur in the life of any plant or animal. Both 

 plants and animals breathe; they oxidize their foods to release 

 energy, carbon dioxide being given off as the result of the union of 

 the carbon in the foods with the oxygen of the air (or of the air dis- 

 solved in water) . Both plants and animals digest their food ; plants 

 may do this in the cells of the root, stem, and leaf. Digestion 

 must always occur so that food can be moved in a soluble condition 

 from cell to cell in the plant's body, and it must take place in an 

 animal for precisely the same reason. 



Assimilation. — The assimilation of foods, or making of foods 

 into living matter, is a process about which very little is known. 

 We know it takes place in the living cells of plants and animals. 

 But how foods are changed into living matter is one of the mysteries 

 of life which have not yet been solved. 



Excretion. — With the building and repair processes there is 

 always waste, in both plants and animals. When living plants 

 breathe, they give off carbon dioxide. In the process of starch 

 making, oxygen might be considered the waste product. Water is 

 evaporated from leaves and stems. The leaves fall and carry 

 away waste mineral substances which they contain. 



Reproduction. — Finally, both plants and animals have organs 

 of reproduction. We have seen that the flower gives rise, after 



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Poppy Pine Street pohfo 



Section through seeds, showing embryos. 



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pollination, to a fruit which holds the seeds. Each seed holds 

 an embryo. Thus the young plant is doubly protected for a 

 time and is finally thrown off with enough food to give it a start 

 in life. In much the same way we shall find that animals re- 

 produce, either by laying eggs each of which contains an embryo 

 and food to start it in life or, as in the higher animals, by holding 



