Summary of the Functions of Green Plants.--The processes which we have just described (with the exception of food making) are those which occur in the lives of any plant or animal. All 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. 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. [Illustration: Leaf of sundew closing over a captured insect.] [Illustration: The Venus fly trap, showing open and closed leaves.] Plants with Special Digestive Organs.--Some plants have special organs of digestion. One of these, the sundew, has leaves which are covered on one side with tiny glandular hairs. These attract insects and later serve to catch and digest the nitrogenous matter of these insects by means of enzymes poured out by the same hairs. Another plant, the Venus fly trap, catches insects in a sensitive leaf which folds up and holds the insect fast until enzymes poured out by the leaf slowly digest it. Still others, 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. [Illustration: 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.)] 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 _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 protecting 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.