THE SIGNIFICANCE OF CHLOROPHYLL 21 



green plants is derived entirely from the atmosphere, 

 in which it is found in the form of what is popularly 

 called " carbonic acid gas/' but which is more correctly 

 named " carbon dioxide " (C0 2 ). In most green plants 

 there are tiny pores or mouths, called " stomata " (Gr. 

 stoma, a mouth), which occur in great numbers in the 

 epidermis of the leaves and green stems, and it is by 

 means of these openings that carbon dioxide is admitted. 

 In completely aquatic plants there are no stomata, but 

 in their case the carbon dioxide in solution in the water- 

 is absorbed through the cell-walls. When we examine 

 the cells of the green part of a plant under the micro- 

 scope, we see that the colouring matter, chlorophyll, 

 is not uniformly diffused through the cells, but is con- 

 fined to little bodies of protoplasm which are denser 

 than the colourless protoplasm of the cells. These tiny 

 bodies are saturated with chlorophyll ; they are variously 

 named " chlorophyll-corpuscles," " -granules," " chloro- 

 plastids." or " chloroplasts." We shall know them by the 

 last-mentioned term. In Fig. 8 we have a diagram of 

 cells containing chloroplasts, some of which are dividing, 

 for they multiply by fission. The little bodies inside the 

 chloroplasts are starch, and the chloroplasts are shown 

 to be tiny chemists engaged in the manufacture of 

 starch. Now, starch is a carbon compound; it is com- 

 posed of carbon, hydrogen, and oxygen, its chemical 

 formula being C 6 H J0 5 . By what manner of alchemy 

 do the chloroplastic chemists produce this compound ? 

 Be it noted, the process involves the conversion of the 

 inorganic into the organic, which is a remarkable feat. 

 Remembering the constitution of starch, we can see that 

 two out of the three elements required for its formation 



