12 TYPES OF BRITISH PLANTS. 
The material is called cellulose, and the only agency that 
can make it is the jelly inside. This wall is just the 
workshop building, and the workman is the jelly inside. 
This is proved by the fact that the wall without the jelly 
is dead, but in the lower plants we can sometimes see the 
jelly go out from the cell, and build itself a fresh wall 
elsewhere. 
Before we go further and examine the various altera- 
tions that this wall may undergo, we must know some- 
thing more (nobody knows very much) about this extra- 
ordinary jelly that can build up plants. The name given 
to it 1s protoplasm, and it looks like raw white of egg. 
Now wherever life is, whether in yourself, in other 
animals, or in plants, this jelly is found, nor is there 
anything known which can make it but protoplasm itself. 
No chemist, for instance, has yet made it in a laboratory, 
and by this jelly, in some way or other, are built up 
all the living things whose study we know as Natural 
History. It is the colourless and transparent basis of all 
life. 
As to its composition, it is almost entirely made up of 
three common gases, nitrogen, oxygen, and hydrogen, and 
the common solid carbon, but there is always a trace of 
sulphur and of certain other minerals. 
This jelly lies on the cell-wall and steadily builds it up, 
putting in fresh material in the interstices, and thereby 
stretching it until it reaches its full intended size. 
Now let us go back for a moment to the cell-wall, and 
see what may happen to it. It may take up two modified 
forms, both useful to a plant in many ways. The wall 
may become hard and woody, giving strength and tough- 
ness, This is called lignification. Or it may become 
cork, and then it is impenetrable to water. A covering 
