246 ZY(;\KMATACEAE 



PLATE I 



Ri PRoiu cTivii Structlkls oh Zvgxemataceae 



Fig. I. — Akinetes of Spirogyra jucrgensii from Crystal Springs, Mis- 

 sissippi, y\pril, 1925. The usual form of akinetes in this species is similar to 

 that of the vegetative cells. Fig. 2. — Akinetes of a Zygnema found at 

 Arcadia, Florida, February, 1931. Fig. 3. — Akinetes and zygospore of Spiro- 

 gyra jarlotvii from Topinohee, Michigan, July, 1934. Figs. 4-5. — Vegetative 

 cell and two aplanospores of Spirogyra wrightiana from Parahiba, Brazil, 

 July, 1934. Fig. 6. — Vegetative cell and two aplanospores of Zygnema frig- 

 idum from Smithville, Oklahoma, May, 1932. Fig. 7. — Aplanospores of 

 Spirogyra pratensis from Charleston, Illinois, May, 191 2. On two of the spo- 

 rangia figured are outgrowths that suggest the initials of conjugating tubes. 

 In many species these outgrowths are alternately or spirally arranged in suc- 

 cessive cells. When present they occur in only some of the sporangia. 

 Fig. 8. — Zygospores and parthenospores of Zygnema stcllnium from 

 Charleston, Illinois, May, 1912. This camera-lucida drawing also demon- 

 strates the distance between filaments through which conjugation may take 

 place. Fig. 9. — Aplanospores and zygospores of Z.ygnema cruciatam from 

 Coffeen, Illinois, May, 1915. Note that aplanospores occur in both male 

 and female filaments. Fig. 10. — Four zygospores of Mougeotia drouetii 

 from Fortaleza, Ceara, Brazil, October, 1935. This figure exemplifies sev- 

 eral species in which the cytoplasmic residues form a film enclosing the 

 zygospores. 



