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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 ju, 40 in diameter 12