ZYGNEMA 17 



It may be of historic interest to know that certain species of 

 Zygnema have been classified previously in the genera : Globulina 

 Link 1820; Tendaridea Bory 1822-31; Stellulina Link 1833; 

 Tyndaridea Hassall 1841; Zygogonium Kiitzing 1843; and 

 Thwaitesia Montagne 1845. More recently Czurda (1932) has 

 included among the Zygnemas certain species which are here 

 classified in the genera: Zygogonium, Zygnemopsis, Hallasia, 

 and Pleurodiscus. 



Key to Species of ZYGNEMA 



I. With aplanospores, zygospores infrequent or absent 53 



I. With zygospores, sometimes aplanospores also 2 



2. Zygospores wholly or largely in the conjugating tubes. ... 3 



2. Zygospores usually in one of the gametangia 26 



3. Median spore wall colorless, yellow, or brown when mature. . 4 



3. Median spore wall blue when mature 17 



4. Zygospores globose to ovoid 5 



4. Zygospores compressed, at right angles to the tubes 22 



5. Diameter vegetative cells less than 20 /u. 6 



5. Diameter vegetative cells usually 20 to 30 /a 8 



5. Diameter vegetative cells usually 30 to 40 /a 15 



5. Diameter vegetative cells more than 40^1 16 



6. Vegetative cells 8-12 /a in diameter, i. Z.oveidanum 



6. Vegetative cells 12-16;^. in diameter 7 



6. Vegetative cells 16-20/x in diameter, 



spores, scrobiculate 4. Z. decussatum 



6. Vegetative cells 16-20 ft in diameter, 



spores, smooth 91. Z. gangeticum 



7. Median spore wall scrobiculate 2. Z. carterae 



7. Median spore wall smooth ^- Z. laevisporum 



8. Median spore wall a single layer 9 



8. Median spore wall of 2 layers 14 



9. Zygospore median wall smooth 23. Z. czurdae 



9. Zygospore median wall scrobiculate, pits less than 4/x 10 



9. Zygospore median wall scrobiculate, pits more than 4 ft 13 



9. Zygospore median wall reticulate 14. Z.pseudopectinatum 



10. Diameter cells 20-21 ix, lateral con- 

 jugation through end walls 5. Z. himalayense 



10. Diameter cells 20-30 a*., conjugating tubes of usual form. . . 11 



II. Spores usually less than 40 ju, in diameter 12 



