GREEN ALGAE 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 commonly seen in our lakes, 

 ponds, and streams. 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 



