GREEN ALGAB 301 
plants, as in Gleocapsa, or remain as a part of a close colony, as 
in Oscillatoria and other forms where the cells of a colony are 
closely associated. In filamentous forms the method of multi- 
plying filaments by means of harmogonia may be classed as a 
method of reproduction. In this case a filament breaks into 
segments which separate and establish new filaments. The 
filament may be segmented by heterocysts or by the death of 
ordinary working cells. 
The simplicity of plant body, cellular structures, and methods 
of reproduction makes the Cyanophyceae the simplest of all 
groups of independent plants now in existence. The absence 
of chloroplasts and a well-defined nucleus and cytoplasm clearly 
distinguishes them from other groups of independent plants. 
But in the group some advancement is shown. The formation 
of a colony in which the cells are closely associated looks forward 
toward the formation of multicellular plants in which the cells 
are very intimately associated. Also the differentiation of the 
cells of a colony into ordinary working cells, heterocysts, and 
resting cells suggests the differentiation of cells in multicellular 
plants into tissues. 
Green Algae (Chlorophyceae) 
The Green Algae are the Algae most commorly seen in our lakes, 
ponds, andstreams. They usually have only one pigment, chloro- 
phyll, and their green or yellow-green color is usually quite 
distinct from that of the Blue-green Algae. Some of the Green 
Algae are microscopic and some form colonies or multicellular 
plant bodies that are clearly visible to the naked eye. Although 
they are small plants, large numbers of them commonly occur 
together, forming scums or tangles of filaments that are conspicu- 
ous. Most of them live in the water but some live on moist 
earth, rocks, or wood, and a few forms can endure periods of 
drought. A few forms live in salt water, but nearly all are fresh 
water plants. 
The Green Algae differ from the Blue-green Algae not only 
in color but also in a number of other ways. Gelatinous sub- 
stances are secreted in abundance only in the lowest forms of 
the group, and consequently Green Algae do not commonly 
form gelatinous masses. They have chloroplasts, and the 
