TAXONOMY 
189 
Spirogyra has also a process of sexual reproduction known as 
conjugation. This process occurs normally from March to June 
and July, but can be induced in the laboratory by allowing the water 
Fig. 77. — Spirogyra sp. A, terminal portion of vegetative filament; B, stages 
of scalariform conjucation; C, preparation for lateral conjugation; D, zygospores 
formed by lateral conjugation. (Gager.) 
in the vessel in which it is growing to slowly evaporate. Two fila- 
ments arrange themselves side by side, and the cells lying opposite 
each other undergo internal changes so as to form gametes or sexual 
