THE CELL AND ITS CONTENTS 13 
of such cells to a plant acts as an overcoat in the winter, 
and in the summer it prevents the heat from drawing 
away too fast the water which is the plant’s life-blood. 
Further, if we examine cells of all kinds we shall find 
that in many the wall is greatly thickened to bear the 
strain of winds or the weight of the plant itself. One 
minute cell would have of course no effect, but when in 
thousands of these workshops side by side the same task 
is going on, you will see how rapidly a plant may be 
strengthened. In some cells the wall is not thickened 
everywhere, but circular or spiral rings are drawn around 
it on the inside, or, sometimes, the protoplasm forces 
material through and builds up ridges upon the outer 
surface of the cell, all in accordance with the unseen 
wonderful design. 
These two elements, the wall and the jelly, are all that 
we can be sure of finding i in every living cell, and we can 
now pass to features which we may meet. 
In all the cells of the higher plants there is a thicken- 
ing of the jelly at one point, and this is called the nweleus. 
What its functions are we do not know, and all we can 
say is that important changes in the cell are always first 
indicated in the nucleus, e.g. when the cell is about to 
divide. One may perhaps consider it as the foreman of 
the workmen in that particular workshop. 
We now come to the most important machine in the 
plant factory, and this is to be found in the cells of 
practically all the green parts of a plant, especially in 
the leaves. Round the edge of the wall we see little 
patches of bright green protoplasm, and these are known 
—and the names should be remembered—as chlorophyll 
corpuscles. The word chlorophyll simply means “green 
leaf.” In Chapter IV. we shall see these corpuscles at 
