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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 secondary
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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