Cytology and Movements of the Cyanophycece . 281 



shown to be made up of cell walls surrounding groups of 

 cells as in the forms where the sheath swells into a jelly. 



In Oscillaria this sheath gelatinizes and is mostly dis- 

 solved away by the water in which it lives, leaving only the 

 inner or last-formed walls directly investing the protoplasts. 

 In younger trichomes, or those which have not been greatly 

 disturbed, the sheath may be still more or less evident. It 

 has a very faint tint after the action of eosin and other pro- 

 toplasmic stains. When not completely dissolved away by 

 the water, it may be demonstrated after mordanting with 

 glacial acetic acid, and staining with carbol fuchsin or 

 methyl blue. It is this stainability of the gelatinized portion 

 of the outer wall, or what may remain of it, that has led 

 observers in the past to think that a protoplasmic pellicle 

 existed as a sheath around the outer wall of the trichome 

 and caused a peristaltic motion in the organism. If such 

 organisms be stained with acid hsematoxylin, this thin coat 

 of gelatin will take a deep reddish blue color, which will also 

 be the result upon the gelatinous envelope if Nostoc or other 

 such form be similarly treated, while the undoubted proto- 

 plasmic cell contents are stained quite differently. Cylin- 

 drospermum is encased in a protective layer of jelly-like 

 consistency. The layer may be very thin, through partial or 

 complete solution as in Oscillaria, or it may be thick enough 

 to completely cover the ciliary processes (Fig. 74). This 

 gelatinous covering is often "heaped up" around the spores 

 and heterocysts (Fig. 56) where it sometimes frays out in 

 irregular finger-like processes. It sometimes is weakly 

 stained by eosin, but the color immediately disappears when 

 the object is immersed in water. 



By carefully manipulating the source and direction of the 

 light, various markings may be found on the walls of the 

 Oscillariacese. In some, definite cross lines are easily seen, 

 averaging from five to seven striae to each cell (Fig. 41), 

 while in others the lines run longitudinally (Fig. 42). In 

 optical section, the walls of the cells of Oscillaria show fine 



