is allowed to dry on the paper, it often leaves a bright
blue stain, due to the blue pigment in the cells of the filament. This
blue color can also be extracted by pulverizing a quantity of the
dried plants, and pouring water over them, the water soon becoming
tinged with a decided blue. If now the water containing the blue
pigment is filtered, and the residue treated with alcohol, the latter
will extract the chlorophyll, becoming colored of a yellow-green.

The microscope shows that the filaments of which the mass is
composed (Fig. 6, _B_) are single rows of short cylindrical cells of
uniform diameter, except at the end of the filament, where they
usually become somewhat smaller, so that the tip is more or less
distinctly pointed. The protoplasm of the cells has a few small
granules scattered through it, and is colored uniformly of a pale
blue-green. No nucleus can be seen.

If the filament is broken, there may generally be detected a
delicate, colorless sheath that surrounds it, and extends beyond the
end cells (Fig. 6, _c_). The filament increases in length by the
individual cells undergoing division, this always taking place at
right angles to the axis of the filament. New filaments are produced
simply by the older ones breaking into a number of pieces, each of
which rapidly grows to full size.

The name "oscillaria" arises from the peculiar oscillating or swinging
movements that the plant exhibits. The most marked movement is a
swaying from side to side, combined with a rotary motion of the free
ends of the filaments, which are often twisted together like the
strands of a rope. If the filaments are entirely free, they may often
be observed to move forward with a slow, creeping movement. Just how
these movements are caused is still a matter of controversy.

The lowest of the _Cyanophyceae_ are strictly single-celled, separating
as soon as formed, but cohering usually in masses or colonies by means
of a thick mucilaginous substance that surrounds them (Fig. 7, _D_).

The higher ones are filaments, in which there may be considerable
differentiation. These often occur in masses of considerable size,
forming jelly-like lumps, which may be soft or quite firm (Fig. 7,
_A_, _B_). They are sometimes found on damp ground, but more commonly
attached to plants, stones, etc., in water. The masses vary in color
from light brown to deep blackish green, and in size from that of a
pin head to severa