204 
F r i ts c li, Stiidies 011 Cyanopliyceae. 
ceable that all tlie individual pairs of cells, which are tlius eacli 
enveloped by a common cell-sheath, lie in one direction; this 
sliows tbat division is prevalent in this direction. The mucilage 
investment of the whole colony is well-marked in stained material 
and projects only very slightly beyond the general contour of 
the aggregate of cells. 
(d) Oscillaria and Lynghya. In the genus Oscillaria , which 
is of considerable interest from the point of view of the present 
paper, it was found convenient to examine a species with fairly 
broad filamentsj as such tend to rnake the recognition of details 
of structure in the investment rather more easy; the following 
observations therefore in the nrain refer to Oscillaria Fröhlich n. 
The cells which constitute the hlaments of this species are flat, 
generally several times broad er than they are long (cf. hg. 11) 
and the colourless septurn between adjacent cells is only of very 
sliglit width; when the cell-contents are very granulär it is almost 
impossible to recognise the delimitations of the individual proto- 
plasts, as the granules tend to aggregate about the region of 
the septa. The whole row of cells or hlament is liere enclosed 
in one general sheath, which is liowever quite evidently merely 
due to the colierence of the individual cell-sheatlis of an Ana- 
haena or Nostoc. In correspondence with the slighter develop¬ 
ment of the transverse- septa the sheath is not split during 
division, but remains as one continuous whole round the entire 
row of cells. HoAvever the sheath still sliows its composite 
origin, in that it is slightly constricted at each point of Separa¬ 
tion of two contiguous cells (hg. 11, c. s.); tliese contrictions- 
run transversely right round the hlament and. give rise to a 
rough stratihcation in surface view. The colourless inner invest¬ 
ment of eacli cell (hg. 11, i. i.) is rather better seen laterally 
(i. e. on the inner side of the sheath) and is generally very 
readily visible at the apex of the hlaments. 
In the year 1897 two papers, dealing with the. structure of 
the cen-membrane and the movements of Oscillaria were publis- 
hed (Dorrens 97, Kolkwitz 97), but the subject-matter con- 
tains very little bearing on the present paper. The out er ivalls 
(i. e. the colierent cell-sheath) show a reticulate structure ac- 
cording to Correns, when treated in a certain way, and in 
connection with this, the following statement of this obseiwer 
is of some interest here: „Bei Aveit geöffneter Irisblende sieht 
man ein rotes Netz auf farblosem Grunde, schmälere oder 
breitere farblose Streifen laufen den Ansatzlinien der Scheide¬ 
wände entlang“ (p. 139). Tliat is to say the parts of the 
colierent cell-sheath, Avliicli lie opposite the lines of Separation 
of the protoplast (the region, Avhere the cell-slieatli splits on 
division in A/nabaenal) , show a different structure to tliat of 
the remainder of the sheath. 
Treated Avith Vesuvin the cell-slieatli of an Oscillaria be- 
comes very prominent and the inner investment also seems to 
take on a faint brown colouration, although this appeärance 
