APPENDIX A 



599 



The Blue-green Algae (Myxophyceae) consist of single cells or of colonies of 

 similar cells surrounded and held together by a gelatinous sheath (Figs. 26.2 and 

 A.l). The colonies may be spherical, platelike, or filamentous in form. The most 

 distinctive feature of this group, shared only with the bacteria, is the absence of 

 a definite nucleus in the cell; there is merely a clearer central portion of the 

 protoplasm that seems to have some of the functions of a nucleus. The cells also 

 lack plastids. In addition to chlorophyll the Myxophyceae contain a blue-green 

 pigment (phycocyanin), and sometimes red, yellow, purple, or brown pigments. 

 The Red Sea gets its name because of a red alga that is a member of the blue-green 





• *oa 







slJl 



Fig. A.l Blue-green algae. {From Sinnott, Botany, ±th ed.) 



group. Cell division takes place by simple fission — a process rare among higher 

 forms; sexual reproduction does not occur. There are no motile cells. 



Considering their simple structure, simple mode of reproduction, and the fact 

 that they store carbohydrates as glycogen (like animals) instead of as starch (like 

 most plants), the blue-greens seem to be only distantly related to other kinds 

 of green plants. It may be that they are the simplest, most primitive cellular 

 organisms living today. 1 Yet they flourish alongside of more advanced types of 

 plants, and often dominate the plankton flora of ponds, lakes, and the sea at 

 certain times and places. Some species grow on the moist surfaces of soil, rocks, 

 and tree trunks. 



1 The bacteria (a group of fungi) are even simpler in structure, but because they lack 

 chlorophyll and, except for a few chemosynthetic species, are dependent upon other 

 organisms for their food sources, most of them are probably of later origin and special- 

 ized by degeneration. Their similarities to the blue-greens suggest some sort of rela- 

 tionship, and they may be an offshoot from primitive blue-green algae. 



