lly separating it with needles, a cover
glass may be placed over the preparation, and it is ready for
examination. When magnified, the green film is found to be composed
of minute globular cells of varying size, which may in places be
found to be united into groups. With a higher power, each cell
(Fig. 11, _A_) is seen to have a distinct cell wall, within which is
colorless protoplasm. Careful examination shows that the chlorophyll
is confined to several roundish bodies that are not usually in
immediate contact with the wall of the cell. These green masses are
called chlorophyll bodies (chloroplasts). Toward the centre of the
cell, especially if it has first been treated with iodine, the
nucleus may be found. The size of the cells, as well as the number
of chloroplasts, varies a good deal.

With a little hunting, specimens in various stages of division may
be found. The division takes place in two ways. In the first
(Fig. 11, _B_), known as fission, a wall is formed across the cell,
dividing it into two cells, which may separate immediately or may
remain united until they have undergone further division. In this
case the original cell wall remains as part of the wall of the
daughter cells. Fission is the commonest form of cell multiplication
throughout the vegetable kingdom.

The second form of cell division or internal cell division is shown
at _C_. Here the protoplasm and nucleus repeatedly divide until a
number of small cells are formed within the old one. These develop
cell walls, and escape by the breaking of the old cell wall, which
is left behind, and takes no part in the process. The cells thus
formed are sometimes provided with two cilia, and are capable of
active movement.

Internal cell division, as we shall see, is found in most plants,
but only at special times.

Closely resembling _Protococcus_, and answering quite as well for
study, are numerous aquatic forms, such as _Chlorococcum_ (Fig. 12).
These are for the most part destitute of a firm cell wall, but are
imbedded in masses of gelatinous substance like many _Cyanophyceae_.
The chloroplasts are smaller and less distinct than in
_Protococcus_. The cells are here oval rather than round, and often
show a clear space at one end.

[Illustration: FIG. 12.--_Chlorococcum_, a plant related to
_Protococcus_, but the naked cells are surrounded by a colorless
gelatinous envelope. _A_,