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26 ZYGNEMATACEAE
pitted; pits 5-6 /i in diameter, 1.5-3M apart, the inner layer densely and
minutely verrucose. (PI. Ill, Fig. 5.)
United States: Oklahoma.
16. Zygnema laetevirens Klebs 1886. Untersuch. Bot. Inst.
Tubitigen. 2, p. 333, PI. 3, Fig. 14.
Vegetative cells 27-34^1 x 40-90 /x; conjugation scalariform; zygospores
formed in the conjugating tubes, globose, 40-55 ^ in diameter,
or ovoid, 34-41/4 x 54-68 /a; median spore wall chestnut brown, of 2
layers, of which the inner is finely verrucose, the outer scattered-scrobic-
ulate. It is probable that the ornamentation of the inner median wall
arises from granules formed between the 2 layers. The same may be
true of Numbers 9 and 15.
United States: Indiana; Ohio; Mississippi; Alabama.
Europe; Australia; China (L. C. Li Coll.).
Spores may be yellow before the verrucose markings of the inner
median wall appear. The Indiana specimens contained many parthenosporcs
similar to the zygospores but smaller.
17. Zygnema pectinatum (Vaucher) Agardh 18 17. Synopsis
Algarum, p. 102.
Vegetative cells 30-36 yu, x 25-120 a^; conjugation scalariform, rarely
lateral; zygospores formed in the conjugating tubes, globose to ovoid,
35-44)". x ju.; 40-54 median spore wall brown, scrobiculate; pits about
2-7, li. in diameter; aplanospores ovoid or cylindric, 30-38 /", x ^0-60 ix;
walls similar. (PI. Ill, Fig. 6.)
United States: Generally distributed eastward from Minnesota, Ne-
braska, Oklahoma, and Louisiana.
Widely distributed in Europe, Asia, Africa, and South America.
18. Zygnema excrassum Transeau 1934. Tratis. Amer. Micros.
Soc. 53, p. 209, PI. 17, Fig. 14.
Vegetative cells 32-36 ^ x 32-80 a^; conjugation scalariform; zygo-
spores formed in the conjugating tubes, usually ovoid, rarely globose
(40-) 50-60 )Lt X 50-7o(-8o)/a; median spore wall brown, scrobiculate;
pits 3-4 M in diameter and about the same distance apart; aplanospores
cylindric-ovoid, nearly filling the sporogcnous cells. (PI. Ill, Fig. 7.)
United States: Oklahoma; Illinois; Iowa; Mississippi; Alabama.
19. Zygnema neopectinatum Transeau 1934. Trans. Amer.
Micros. Soc. 53, p. 209, PI. 17, Fig. 7,
Vegetative cells 40-45 /m x 40-85^1; conjugation scalariform; zygospores
formed in the conjugating tubes, ovoid to globose, 45-54 M x