THE LIVING PLANT 33 



manufacture food materials in the daytime only. Briefly the 

 process is as follows : Water is taken up by the root-hairs and 

 transported to the leaves. Carbon dioxide in the air is taken 

 in by the leaves through the stomata. The water and 

 carbon dioxide are broken up and united in the leaves to 

 form sugars, and oxygen, a waste product of the process, 

 is given off. The process takes place extensively in the 

 palisade-cells of the leaves through the action of chlorophyll, 

 a greenish-colored oily liquid, for the production of which 

 light is necessary. It is well known that plants grown in the 

 dark lack chlorophyll. This explains their pale coloring. 

 It will be seen that light supplies the energy for photo- 

 synthesis, that chlorophyll does the work, and that carbon 

 dioxide and water are the materials from which the sugars 

 are made. The process is complicated as there are several 

 chemical steps before sugar is manufactured. 1 The amount 

 of sugar manufactured is considerable but varies with different 

 plants. Other forms of sugar, as well as grape sugar, are 

 found in the plant. Protein materials also are manufactured 

 by plants, and certain fats and oils. The manufactured 

 carbohydrate food material is transported to the different 

 parts of the plant in the form of sugars, which are soluble, and 

 is stored in the form of starches, which are insoluble. 



It will be seen that the chemical process in photosynthesis 

 is the opposite of that in respiration, and also that the 

 materials used and waste products in photosynthesis are 

 different than in respiration. It should be remembered that 

 in respiration, oxygen (0) is used, and carbon dioxide (CO 2 ) 

 is given off day and night, while in photosynthesis, carbon 

 dioxide (C0 2 ) is used and oxygen (O) is given off in the day- 

 time only. During the night, when respiration only is taking 

 place, a small quantity of carbon dioxide (CO 2 ) is given off 



J The chemical reaction may be summed up, however, as follows: Carbon 

 dioxide 6CO 2 plus water (6H 2 O) form grape sugar (CsHuOe) , and oxygen 

 (6O 2 ) is a waste product. 



