ANATOMY OF THE CELL. 3 
Cells vary as much in form as in size; those without a 
membrane incline to the spherical shape, since the protoplasm 
composing them is in a half-liquid state. Many swarm-spores 
are pear-shaped, but they generally assume a spherical form on 
coming to rest. The forms of some naked cells are subject 
to rapid change, for example the spores of Bangia, a red 
seaweed. 
In all the higher plants, new cells are formed by the growth 
of walls across the cavities of the old cells. The new walls 
join the old at certain angles, and when the cells are young, 
they are inclined to a hexagonal form. As growth continues 
the form is lable to change in various ways. If the cell should 
grow equally fast in all its parts, it would tend to retain its 
original form. This very rarely happens, and even when it 
does, the shape of such a cell is influenced in a greater or less 
degree by the manner of growth of those surrounding it, as the 
growing wall is flexible and its shape easily changed by pressure 
or traction from without. 
The individuality of the cell is shown by the fact that each 
has its own predetermined manner of development. All young 
cells of any plant are, at first, nearly similar in form and size, 
but later on each cell is seen to follow certain laws of growth 
which are, to a certain extent, independent of all external 
forces. From these laws, together with various mechanical 
causes, arises the great variety of form in the cells of ordinary 
plants. The peculiar forms common to certain unicellular 
plants illustrate even better than those of higher ones the 
inherent tendency of cells to grow in a certain manner. 
Examples of these are the branched mycelium of Mucor, 
which is one-celled till reproduction takes place; also the 
many singular shapes assumed by one-celled algae. Of the 
latter, Caulerpa is perhaps the most wonderful, where stem, 
leaf, and root of higher plants are simulated by the branching 
of a single cell. 
