Cytology and Movements of the Cyanophycee. 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 hzmatoxylin, 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 
Oscillariaceze. In some, definite cross lines are easily seen, 
averaging from five to seven strie 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 
