CHAPTER THIRTEEN 



THE GENUS SPIROGYRA LINK 1820 



The species of Spirogyra are known to more people than those 

 of any other genus of the filamentous green algae. For many 

 years they have been seen and named in biology classes in sec- 

 ondary schools and colleges. They occur on all the continents and 

 larger islands in fresh-water ponds, streams, and lakes. Among 

 the filamentous green algae the genus Spirogyra ranks next to 

 Oedogonium in the number of described species. 



In the following pages, 275 species are described, and it is 

 highly probable that this number will be greatly increased as soon 

 as habitats are visited repeatedly and collections are made by 

 trained personnel. Most of our present knowledge is based on 

 chance collections. Since we know that the fruiting period of 

 many species is less than a fortnight, only repeated visits to the 

 same station possibly can secure identifiable specimens of all the 

 species present. 



Professor Jean Massart once remarked, "Why waste your time 

 on Spirogyras — there are no species in that genus." It is true that 

 there are some highly variable species among them, but I suspect 

 that most of the species will be found to be remarkably uniform 

 when once they have been described adequately. The older de- 

 scriptions were quite incomplete and gave few details concerning 

 spore walls, conjugating tubes, and even spore forms. Conse- 

 quently, many diverse specimens were classified as belonging to 

 the same species. 



The filaments of the Spirogyras are composed of cylindric cells, 

 all very much alike except the first or basal cell which may 

 develop as a rhizoid and anchor the filament at least during its 

 early development. The vegetative cells of larger species often 

 appear barrel-shaped under the microscope, and have been thus 

 described and figured. This appearance usually is due to the 

 pressure of the cover glass. Measurements of the diameters of 

 vegetative cells should be made at the partition walls. Czurda 



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