PHYSIOLOGY OF TtfE COTTON PLANT 25 



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

 down into carbon and oxygen. % 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 C0 2 + 6 H 2 = C 6 H 12 6 + 6 2 

 carbon dioxide water photosynthate 1 oxygen 



Most of the sugar thus formed is quickly converted into 

 starch, probably in accordance with the following reaction : 



C 6 H 12 C = C 6 H 10 5 H 2 



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 formation 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 breaking 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 grajns absorb both the carbon dioxide 

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



1 This term is being applied in the recent plant physiologies to the 

 carbohydrate produced as the result of photosynthesis. 



