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 compara- 

 tively 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 charac- 

 teristic 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 fila- 

 ments. Usually the progametangia divide into two unequal gam- 

 etangia — 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 develop- 

 ment 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. 



231 



