THE GROWING PLANT 



35 



chlorophyll bodies absorb energy in the form of light. 

 This energy the chlorophyll body uses to take to pieces 

 the carbonic acid, mineral salts and water absorbed from 

 the air and the soil, and to recombine them into foods 

 which can be used by the protoplasm in making new parts 

 and repairing waste (photosynthesis). Until this food 

 manufacture commences, no new plant substance has been 

 formed. It is true that new cell-walls and new protoplasm 



I I ■"" ep 



Fig. 15. — Cross-section through leaf of beech (Fagus). Ch chlorophyll 

 bodies ; Ep epidermis of upper surface of leaf ; jBp"epidermis of lower 

 surface ; K cells containing crystals ; PI palisade layer ; P vascular 

 bundle ; St breathing pore (stoma) ; I spaces between the cells 

 (intercellular spaces) . Highly magnified. 



may be formed from the food supply of the seed before 

 chlorophyll appears, but until chlorophyll is formed, and 

 photosynthesis begins, the whole plantlet with whatever 

 remains of the seed, when dried, weighs no more than the 

 seed weighed at the beginning. The food material 

 formed in photosynthesis is starch, or some substance of 

 similar composition (sugar or oil), which, after under- 

 going chemical changes if need be, to render it soluble, is 

 distributed throughout the plant to be built up into 

 tissues (assimilation) or to be held as reserve food (14). 



