CHAPTER II.—CELL WALL. 
1. Finer and Coarser Structure of Cell Wall. 
THE wall is a product of the contents and is not an essential 
part of the cell. Its formation occurs in two ways. A naked 
cell may surround itself by a wall, or a cell already possessing 
a closed wall may form a new one which extends through the 
cavity and becomes fixed to the surfaces of the opposite walls, 
the mother or initial cell, as it is called, thus becoming divided 
into two cells. Examples of the former case may be found in 
swarm spores of various plants which either throw off their 
cilia or draw them in, and soon after surround themselves by a 
cellulose wall. The second manner of wall formation is best 
illustrated in the growing regions of ordinary plants. 
Here the first appearance of the new wall on a cross-section, 
as seen by the aid of the strongest lenses, is that of a very, fine 
line or thread stretched across the cavity. This is known to 
result from some action of the protoplasm of the mother cell by 
which cellulose micellae are formed and arranged in such a 
manner as to make a very thin membrane. This is the product 
either of the entire protoplasm of the original cell, or of that 
portion of it which is in near proximity to the newly formed 
wall. In either case it may be said to belong equally to both 
the cells resulting from its formation. At this stage of its 
existence it is known as the primary wall. 
By watching its development it will be readily seen that it 
does not remain long in this condition, but increases in thick- 
ness till it reaches that of the other walls in the growing por- 
tion of the plant. The new cells thus formed now begin to 
increase rapidly in size and to assume those shapes which will 
fit them for their different functions. During this period the 
