THE SEEDLING AND TOUNG PLANT. 85 



the cells. It has been calculated that an oak-tree may 

 have 700,000 leaves, and that 111,225 kilogrammes of 

 water may pass off from its surface in the five months 

 from June to October, and that 226 times its own 

 weight of water may pass through it in a year. 



Now comes the question, What are the salts needed 

 for that so much mechanism should be expended on 

 their accumulation ? To answer this, we must look at 

 the mesophyll cells a little more closely. 



Each of these consists of a thin cellulose cell-wall, 

 lined with colorless protoplasm, which incloses a large 

 sap-cavity (vacuole) ; in the protoplasm are imbedded a 

 number of bright-green, rounded chlorophyll corpuscles, 

 a relatively large nucleus, and a few less conspicuous 

 granules, etc. The cell-sap contains various substances 

 dissolved in water. Some of these substances are salts 

 arfd other materials ready to be made use of ; others are, 

 so to speak, waste products or worked-up materials that 

 are going to be got rid of, or sent to places where they 

 will be made use of, respectively. 



In the colorless protoplasm which lines the interior 

 of the cell-wall and surrounds the cell-sap we find a 

 nucleus and the chlorophyll corpuscles, as said, and a 

 few words must be devoted to the latter. Each chloro- 

 phyll corpuscle consists of a rounded mass of proto- 

 plasmic substance of somewhat spongy texture, contain- 

 ing the peculiar green body, chlorophyll, imbedded in 

 it as in a matrix. These chlorophyll corpuscles are liv- 

 ing organs, and they require food materials water, oxy- 



