PHYSIOLOGY OF TEE COTTON PLANT 25 



dioxide is absorbed by the leaf cells, in which it is broken 

 down into carbon and oj^ygen. The carbon unites with 

 the water which has been absorbed from the soil, the 

 result being the formation of carbohydrates. This process 

 is called photosynthesis. ■ The following equation has 

 been suggested as representing the changes that take place: 



6 CO^ + 6 H,0 = CeHj,Oe + 6 0^ 

 carbon dioxide water photosynthate^ oxygep 



Most of the sugar thus formed is quickly converted into 



starch, probably in accordance with the following reaction : 



I 



GgHigOo = CeHii)05H20 



While the starch is manufactured in the leaves, it can- 

 not be transferred in this form to other parts of the plant 

 for building tissues as starch is not .soluble. Consequently 

 it is later changed back into sugar in which form it- is 

 carried to all parts of the plant, for the forination of car- 

 bohydrate material. 



At the same time that the carbon dioxide is being taken 

 up from the air and decomposed in the plant, an almost 

 equal volume of oxygen is being given off from the leaves 

 as a by-product. 



27. The necessary energy. — The t)reaking down of 

 the carbon dioxide and the formation of carbohydrate 

 materials in the plant, such as sugar and starch, require 

 the expenditure of considerable energy. The plant se- 

 cures this energy from the sunlight. The leaf cells, except 

 •those in the veins, contain small green chlorophyll, bodies. 

 These chlorophyll grains absorb both the carbon dioxide 

 and the sunlight, and with the energy thus received, the 



J- This term is being applied in the recent plant physiologies to the 

 carbohydrate produced as the result of photosynthesis. 



