UTILIZATION OF PLANT FOOD 33 



white or yellowish in color. Grass leaves that have grown 

 under a board or stone are lacking in chlorophyl. 



23. Manufacture of Carbohydrate.- -The raw materials, 

 combining to form the chemical compounds which store 

 this energy, are carbon dioxide and water. The water, as 

 has been noted, comes up from the soil through the roots 

 and stems. The carbon dioxide enters the leaves through 

 small openings on the under side, called stomata (Fig. 3, g). 

 This gas passes into the air spaces (Fig. 3, /) between the 

 cells and finally through the cell wall, dissolving in the cell 

 sap to form carbonic acid. Under the action of the light 

 waves absorbed by the chlorophyl, carbonic acid probably 

 breaks up into formaldehyde and oxygen according to this 

 equation : 



H 2 C0 3 = CH 2 o + 2 . 



The oxygen is given off through the cell walls into the air 

 spaces and out through the stomata. The formaldehyde, 

 dissolved in water, of course, is almost instantly condensed 

 to dextrose, thus: 



GCH2O = CeHwOe. 



The dextrose is acted upon by an enzyme which subtracts 

 water from it and forms starch (Fig. 4, s), thus: 



n C6H12O6 _ n H2O = (C 6 Hio0 5 )n. 



Starch is usually the first visible compound formed in this 

 process of photosynthesis, as the process of chemical synthesis 

 by means of light is called. In some cases, however, the 

 dextrose is changed to sucrose. This process of starch manu- 

 facture goes on during the day only. No synthesis takes 

 place in the dark. 



24. Transfer of Carbohydrates. — Starch in the leaf is 

 only the temporary form of manufactured material. During 

 the day carbonaceous matter is synthesized more rapidly 

 than it can be removed, and tire cells would be clogged with 

 soluble food if it were not changed to an insoluble, concen- 

 trated form for temporary storage. At night when no car- 



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