86 THE OAK. 



gen, etc. for the support of their life processes, just as 

 do the other living parts of the cell e. g., the colorless 

 protoplasm and nucleus. They obtain these from the 

 cell-sap, through the agency of the colorless protoplasm 

 in which they reside. 



In order that they may perform their functions prop- 

 erly, 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 meso- 

 phyll 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 illumi- 

 nated by the sunlight ; moreover, the large intercellular 

 passages which communicate by thousands of stomata 

 with the atmosphere insure their being thoroughly 

 aerated. In addition to allowing the free access of the 

 oxygen of the air, moreover, these intercellular passages 

 admit of the small quantities of carbon dioxide in the 

 atmosphere also reaching the chlorophyll corpuscles. 

 Oxygen and carbon dioxide, therefore, are found dis- 

 solved 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 sun- 

 light i. e., energetic vibrations of the ether which per- 



