19S 
Fritscli, Studies on Cyanopliyceae. 
tively early stage ancl for tlie sake of brevity I sliall designate 
tkem sporogenons filaments as a contrast to tlie purely vege¬ 
tative filaments. 
2. Detailed considerations. 
(a) Anabaena. Wfien pnrely vegetative filaments are exa- 
mined microscopically, as already stated, an enveloping mem- 
brane is readilv evident only between adjacent cells. Sporo¬ 
genons filaments on tlie otber liand exliibit well - marked 
lateral walls to tlie cells, Avfiicfi appear as a fairly tliick 
dark line, wfien focussed so as to be seen in optical section 
(fig. 4 and 5). If sucli filaments are stained Avitfi an aqueous 
solution of lodine tlie following pecnliar structure appears (fig. 5). 
Tlie longitudinal (lateral) Avails of eacli cell are sliarply marked 
off from one anotfier in adjacent cells (fig. 4, 5, c. s.) and appear 
separated from one anotfier by tlie colomdess area, wfiicfi repre- 
sents tlie transverse Avall between tlie two cells concerned (fig. 5. 
t. s.). Tfiis latter is bounded laterally by a faint, sligfilty con- 
cave liniit (cf. fig. 3 b, t. s.). Oareful examination reveals tlie 
fact, tfiat tlie free ends of tlie lateral Avails are connected witfi 
one anotfier transversely by a very delicate line (1 in Fig. 5), 
running apparently rigfit round eacli end of tlie protoplast, tlie 
transverse wall (t. s.) between adjacent cells, separating tfiese 
lines from one anotfier. In otfier words, looking at sucli stained 
sporogenous filaments under a higfi power, tfieir appearance is 
sucli as to give one tlie Impression tfiat tlie lateral Avails of 
eacli cell form part of a fiollow sfieatfi-like cylinder around tlie 
sarne. tlie open ends of wfiicfi give rise to tlie above-mentioned 
line, connecting tlie free ends of tlie lateral walls. Eacli cell of 
tfie filament is tfius surrounded by a special cylindrical sfieatfi 
of its oAvn (= cell-sfieatfi, fig. 5 and 8, c. s). wfiicfi, AA'lien diAÜ- 
sion of tfie cells takes place, is simply split into tAA^o fresfi 
sfieatfis by tfie development of a colourless intercellular mass 
(fig. 3 a, b). Wlien a cell of Anabaena is about to di au de an 
indentation of tfie lateral walls (= cell-sfieatfi) appears at about 
tfie middle of tfieir lengtfi, giving rise to a constriction, running 
round tfie middle of tfie motfier-ceU (fig. 3 a). At tfie same time 
a very tfiin colourless strip (cf. fig. 3 a, t. s.), appears in tfie cell- 
contents on tfie same level as tfie constriction of tfie eell-Avall 
(cylindrical sfieatfi) and, as tfiis strip graduaUy increases in 
Avidtfi (fig. 3 b) and develops into tfie intercellular colourless area, 
tfie new cells move apart from one anotfier and tfie individual 
cylindrical sfieatfi of eacli becomes distinct. Tfie details of tfiis 
process are difficult to observe and I am not at present pre- 
pared to say, wlietfier tfie Splitting of tfie sfieatfi is a purely 
pfiysical process or wlietfier it is tfie result of some special 
structural cfiange. In fiis recent preliminary paper on tfie cell- 
structure of Cyanophyceae "Wäger (04, p. 406) describes tfiis 
