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 ofthese 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. Hach 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 
