CIRCULATION AND USES OF FOOD BY PLANTS 103 



called pitcher plants, use as food the decayed bodies of insects 

 which fall into their cuplike leaves and die there. In this respect 

 plants are like those animals which have certain organs in the 

 body set apart for the digestion of food. 



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

 into living matter, is a process we know very little about. 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 we have not yet solved. 



Excretion. — The waste and repair of living matter seems to 

 take place 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 

 pollination, to a fruit which holds the seeds. These seeds hold 



The embryos of (a) the morning glory, (b) the barberry, (c) the potato, (d) the 

 four o'clock, showing the position of their food supply. (After Gray.) 



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

 and is finally thrown off in the seed with enough food to give it a 

 start in life. In much the same way we will find that animals 

 reproduce, either by laying eggs which contain an embryo and food 

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

 tecting the embryo within the body of the mother until it is born, 

 a helpless little creature, to be tenderly nourished by the mother 

 until able to care for itself. 



The Life Cycle. — Ultimately both plants and animals grow 

 old and die. Some plants, for example the pea or bean, live but 



