SYNTHESIS, STORAGE AND BREAKDOWN 115 



expressed in terms of heat units, is indicated in the following equa- 

 tion which sums up the process of photosynthesis. 



6C0 2 + 6H 2 + 674,000 calories = C 6 H 12 6 + 60 2 



That is, the synthesis of a gramme-molecule (180 gm.) of sugar 



requires the equivalent of 674,000 calories of heat-energy. It will 



be seen from this equation that 



photosynthesis consists of the 



formation of sugar from carbon 



dioxide and water, energy being 



utilised and oxygen liberated. 



The green pigment of plants, 

 Chlorophyll, is a key substance in 

 photosynthesis. The pigment is 

 located in special protoplasmic 

 bodies, the Chloroplasts, which are 

 restricted to those organs of the 

 plant that are exposed to light : 

 they are especially abundant in 

 the mesophyll of the leaf, which is 

 the chief organ of photosynthesis. 

 Experiment proves that only those 

 parts of the plant that contain 

 chlorophyll can carry on photo- 

 synthesis. To confirm this, varie- 

 gated leaves may be used, and it 

 can be shown that only the green 

 parts of the leaf can conduct 

 photosynthesis. In order to de- 

 tect the occurrence of photosyn- 

 thesis one method is to test for 

 the presence of the end-products. 

 Sugars themselves are not so easily 

 detected as the higher carbo- 



„ Jlt . LJLaj / shows the inclui 



plastid has swollen in water. (After Sachs.) 



plants is very quickly formed 



from the initially-produced sugars. A plant with variegated 

 leaves is exposed to sunlight for several hours, at the end of 

 which time a leaf is to be detached, and the outlines of the yellow 

 and green parts noted. The leaf is dipped in boiling water and 

 then immersed in methylated spirit, which is heated over a water- 



Fig. 76. 



A. Chloroplasts in cells of the leaf of Funaria, 

 showing small starch-grains included in them. 

 B shows stages of division of the chloroplasts. 



hydrate Starch, which in many ^J?,,*^^ starch " grains - after 



