he simplest form of plant life is an undifferentiated individual, all
of its functions being performed indifferently by all parts of its
protoplasm.

The chemical basis of plasmodium is almost entirely composed of
complex albuminous substances, and correlated with this structureless
body are other compounds derived from them. Aside from the chemical
substances which are always present in living matter, and are
essential properties of protoplasm, we find no other compounds. In the
higher organisms, where these functions are not performed
indifferently, specialization of tissues is accompanied by many other
kinds of bodies.

The algae are a stage higher in the evolutionary scale than the
undifferentiated noncellular plasmodium. The simple _Alga
protococcus_[3] may be regarded as a simple cell. All higher plants
are masses of cells, varying in form, function, and chemical
composition.

A typical living cell may be described as composed of a cell wall and
contents. The cell wall is a firm, elastic membrane closed on all
sides, and consists mainly of cellulose, water, and inorganic
constituents. The contents consist of a semi-fluid colloidal
substance, lying in contact with the inner surface of the membrane,
and, like it, closed on all sides. This always is composed of
albuminous substances. In the higher plants, at least, a nucleus
occurs embedded in it; a watery liquid holding salts and saccharine
substances in solution fills the space called the vacuole, inclosed by
the protoplasm.

These simple plants may be seen as actively moving cells or as
non-motile cells. The former consist of a minute mass of protoplasm,
granular and mostly colored green, but clear and colorless at the more
pointed end, and where it is prolonged into two delicate filaments
called cilia. After moving actively for a time they come to rest,
acquire a spherical form, and invest themselves with a firm membrane
of cellulose. This firm, outer membrane of the _Protococcus_
accompanies a higher differentiation of tissue and localization of
function than is found in the plasmodium.

_Haeatococcus_ and plasmodium come under the classes algae and fungi of
the Thallothyta group. The division[4] of this group into two classes
is based upon the presence of chlorophyl in algae and its absence in
fungi. Gelatinous starch is found in the algae; the fungi contain a
starchy substance called glycogen, which also occurs in the liver and
muscles of animals. Stru