Q^ BEGINNEBS' .BOTANY 



Chlorohyll (^"leaf green") is the agent that secures 

 the energy by means of which carbon dioxide is utilized. 

 This material is contained in the leaf cells in tiie form of 

 grains (p. 86) ; the grains themselves are protoplasm, only 

 the colouring matter being chlorophyll. The chlorophyll 

 hoclics or grains arc often most ahundant near the upper 

 surface of the leaf, where tlxcy can secure the greatest 

 amount, of light. Without this green colouring 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 coloured 

 leaves as coleus, have chlorophyll, but it is masked by 

 other colouring matter. This other colouring matter is 

 usually soluble in hot water: boil a coleus leaf and notice 

 that it becomes green and the water becomes coloured. 



Plants grown in clarlcness are yelloiv and slender, and 

 do not reach maturity. Compare the potato sprouts that 

 have grown from a tuber lying in a dark cellar with 

 those that have grown normally in the bright light. 

 The shoots have become slender, and are devoid of cliloro- 

 ph^'ll ; and when the food that is stored in the tuber is 

 exhausted these shoots will have lived useless lives. A 

 plant that has been growTi in darkness from, the seed will 

 soon die, although for a time the little seedling will gro-w 

 very tall and slender. "Why? Light favours the production 

 of chlorophyll, and the chlorophyll is the agent in the mak- 

 ing of the organic carbon compounds. Sometimes chloro- 

 phj^ll is found in buds and seeds, but in most cases these 

 places are not perfectly dark. Notice how potato tubers de- 

 velop chlorophyll, or become green, when exposed to light. 



Photosynthesis. — Carbon dioxide diffuses into the leaf; 

 during sunlight it is used, and oxygen is given off. How 



