THE SEEDLING AND YOUNG PLANT 85 



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 colourless protoplasm, which encloses a large 

 sap-cavity (vacuole) ; in the protoplasm are embedded 

 a number of bright green, rounded chlorophyll cor- 

 puscles, a relatively large nucleus, and a few less con- 

 spicuous granules, &c. The cell-sap contains various 

 substances dissolved in water. Some of these substances 

 are salts and 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 colourless 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 chlorophyll 

 corpuscle consists of a rounded mass of protoplasmic 

 substance of somewhat spongy texture, containing the 

 peculiar green body, chlorophyll, embedded in it as 

 in a matrix. These chlorophyll corpuscles are living 

 organs, and they require food materials, water, oxygen, 

 &c., for the support of their life processes, just as do the 



