214 
Fritscli, Stuclies 011 Cyanopliyceae. 
Fi«-. 10. Basal portion of a ülament of Gloeotricliia natans (Hedwig) 
Baben h?, showing tlie colierent. bnt markedly constricted cell-sheath and 
the basal heterocyst (h). (X about 1600). .. 
Fig. 11. Part of a ülament of Oscillana, Frohhchu , showing^ tlie 
colierent cell-slieatb. Tlie constrictions are ratlier exaggerated. (> 1450.) 
Fig. 12. Part of a ülament of Tolypothrix in tlie living, unstained 
condition, in wüicü no celLsheath is visible witliin tlie external slieatli (?. •$.). 
A small portion of tlie ülament lias died away through injury, leaving tlie 
prominent transverse septa (t. s.). Tlie exposed apices of tlie ülament ai e 
covered by tlie much-tliickened cell-sheatü. (X 1450). 
Fig/13. Small portion of a ülament of Tolypothrix , treated witli 
lodine. The central ülament lias contracted away from tlie external slieatli 
and its colierent, but moniliform cell-slieatli and the innei in\estments of 
tlie protoplasts are now cpiite visible. (X about 1600). 
Fig. 14. Living, unstained ülament of Tolypothrix , illustratmg repeated 
sheath-formation; see text p. 42. (X 1450.) _ . 
Fig. 15. Portion of a ülament of Tolypothrix, treated witli chromic 
acid. ®he ülament lias contracted away from tlie external theath (e. s .): 
the cell-sheath has been dissolved away and only the inner Investment 
remains M i.). Tlie protoplasmic contents have all disappeared except lor 
a few globules in each cell. ( ) 1450.) 
Fig. 16. Small portion of a ülament of Lynghya salina Ktz.. sliowing 
the wide hyaline external slieatli, the colierent cell-sheatli and the deh- 
cate inner investments around the protoplasts. (X 600 about. 
