86 THE OAK 



other living parts of the cell e.g. the colourless proto- 

 plasm and nucleus. They obtain these from the cell-sap, 

 through the agency of the colourless protoplasm in which 

 they reside. 



In order that they may perform their functions 

 properly, however, it is essential that they be exposed 

 to light ; this is effected by their being in cells which 

 are disposed in thin layers, such as we have seen the 

 mesophyll of the leaf to be. In fact, the flat, thin, 

 expanded form of the leaf is a direct adaptation to the 

 end that these chlorophyll corpuscles shall be properly 

 illuminated by the sunlight; moreover, the large in- 

 tercellular passages which communicate by thousands 

 of stomata with the atmosphere ensure their being 

 thoroughly aerated. In addition to allowing the free 

 access of the oxygen of the air, moreover, these inter- 

 cellular passages admit of the small quantities of carbon 

 dioxide in the atmosphere also reaching the chlorophyll 

 corpuscles. Oxygen and carbon dioxide, therefore, are 

 found dissolved with the other materials in the cell- 

 sap which saturates the protoplasm and reaches the 

 chlorophyll corpuscles. 



These facts premised, we are in a position to follow 

 generally the astounding transformations which go on 

 in these millions of chlorophyll corpuscles in the oak- 

 leaf. Carbon dioxide and water exist side by side in 

 the protoplasm of the chlorophyll corpuscle, and rays of 

 sunlight i.e. energetic vibrations of the ether which 

 pervades the universe penetrate into the system. By 



