76 THE MAKING OF THE LIVING MATTER 



which has become an intense green. Save this leaf for 

 a future experiment. Without chlorophyll, the plant can 

 not appropriate the carbon dioxid of the air. 



160. In most plants this chlorophyll or leaf -green 

 is scattered throughout the green tissues in little oval 

 bodies, and these bodies are most abundant near the upper 

 surface of the leaf, where they can secure the greatest amount 

 of light. Without this green coloring matter, there would 

 be no reason for the large flat surfaces which the leaves 

 possess, and no reason for the fact that the leaves are 

 borne most abundantly at the ends of branches, where the 

 light is most available. Plants with colored leaves, as 

 coleus, have chlorophyll, but it is masked by other color- 

 ing matter. This other coloring matter is usually soluble 

 in hot water: boil a coleus leaf and notice that it becomes 

 green and the water becomes colored. 



161. Plants grown in darkness are yellow and slender, 

 and do not reach maturity. Compare the potato sprouts 

 which have grown from a tuber lying in the dark cellar 

 with those which have grown normally in the bright light 

 (Fig. 42). The shoots have reached out for that which 

 they cannot find ; and when the food which is stored in 

 the tuber is exhausted, these shoots will have lived useless 

 lives. A plant which has been grown in darkness from the 

 seed will soon die, although for a time the little seedling 

 will grow very tall and slender. Light favors the produc- 

 tion of chlorophyll. Sometimes chlorophyll is found in 

 buds and seeds, but it is probable that these places are not 

 perfectly dark. Notice how potato tubers develop chloro- 

 phyll, or become green, when exposed to light. 



162. PHOTOSYNTHESIS. Carbon dioxid is absorbed by 

 the leaf during sunlight, and oxygen is given off. We 

 have seen (157) that carbon dioxid will not support animal 

 life. Experiments have shown that carbon dioxid is ab- 

 sorbed and that oxygen is given off by all green surfaces 



