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CHAPTER FOURTEEN
THE GENUS SIROGONIUM KtJTZING 1843
The vegetative cells of the species belonging to this genus
resemble those of certain species of Spirogyra with plane end walls
and several narrow chromatophores. The cell wall, however,
differs in the absence of an appreciable external pectose layer. The
average length of the cell is two to four times the diameter, though
exceptional cells may attain lengths of five to seven diameters.
The described species have from two to ten chromatophores,
which are either straight or only slightly curved, and comparatively
narrow.
Conjugation occurs directly between gametangia, without the
formation of conjugating tubes. Apparently the gametangia on
coming in contact adhere, and the walls in contact change to
pectose and pectic acid. At the edges of the contact disc, a ring
of pectose develops outside the walls. At the same time the walls
of both gametangia grow, and after bending enlarge to a characteristic
form best described by the figures on Plate XL.
The development of the gametangia takes places only from
certain vegetative cells scattered singly or in pairs along the filaments.
Usually the progametangia divide into two unequal gametangia—one
short and one long—and food substances accumu-
late in them. There may be two divisions resulting in a larger
gametangium between two short cells. De Bary stated that the
first type of division resulted in female and the latter in male
gametes; he called the short cells "sterile." However, the development
of gametangia is highly variable in some collections. Appar-
ently progametangia may conjugate without division. Any of the
short cells may become male gametangia, and division into three
cells before conjugation is far less frequent than division into two
unequal cells. As a result of the flexing of the gametangia at the
beginning of a conjugation, successive conjugations in a particular
filament are each with a different filament. Conjugated filaments
thus form a tangled net.
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