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i86 ZYGNEMATACEAE
PLATE XXI
Spirogyra
Fig. I.—5. communis, gametangia and zygospores from Illinois. Fig. i.
—5. intorta, conjugating filaments and zygospores from Szechwan, China.
After Jao. Fic. 3. S. juergensii, typical gametangia and zygospores from
Illinois. Fig. 4. S. singularis, gametangia and zygospores from Illinois.
Fig. 5.- S. gracilis, gametangia and zygospores from Ohio. Fig. 6. S.
jragilis. gametangia and zygospores. Note separation of receptive gam-
etangia following conjugation, from Szechwan. After Jao. Fig. 7. S. sil-
i'icola, gametangia and zygospores from northern Illinois. After Britton.
Fig. 8. S. teodorcsci, gametangia and zygospores from Illinois. Figs. 9-
10. S. vartjormis, vegetative cell, gametangia, and zygospores variously
deformed by the gametangial walls from Cape Town, South Africa.
Fig. II. S. condensata, lateral and scalariform conjugation, vegetative cell,
and zygospores from Charleston, Illinois. Figs. 12-14.—5. pseudovarians,
gametangia, zygospores, and optical section of spore wall from Czecho-
slovakia. After Czurda.