44 THE STORY OF PLANT LIFE 



8. Carbon Assimilation and Photo-Synthesis. 



There are green plants and others not green. It 

 is found that those that are not green have to depend 

 for their nutritive material on green plants. The 

 green colour of such plants is due to the presence of 

 chlorophyll, a pigment manufactured by the chloro- 

 plastids. Chlorophyll is a green or yellow substance 

 contained in chlorophyll granules in the cells of the 

 leaves in particular. When the light is intense these 

 bodies arrange themselves in a certain direction. 

 When the light is normal they expose as much 

 surface as possible to the light. In such circum- 

 stances the sun is shining. The cells containing the 

 chlorophyll granules are in direct communication 

 with spaces or avenues which are connected with 

 openings below on the under-surface of the leaves, 

 generally speaking. From these openings it may be 

 shown that oxygen is being given off, as in the case 

 of the following simple experiment. 



Some Canadian water-weed is placed in a vessel of 

 water. A test-tube full of water is inverted in the 

 vessel and supported by a retort stand so that the 

 bottom of the test-tube is well above the bottom. 

 This is to ensure a good supply of well-aerated water. 

 The basal ends of the stems of the water-weed are 

 then introduced under the test-tube and the apparatus 

 is kept in a good light. Bubbles of gas will be seen 

 to rise from the stems. The gas will rise to the top 



