] i)S I' li tsr li , StiuUes oii ( 'v;iiii>pliyeone. 



tively carly sta^e aiul l'or tho sakc of bicvity I shall dcsignate 

 them sporoo^cnoiis iilaments as a contrast to tlie piircly vc'<2;e- 

 tativf lilamonts. 



2. Detailed •considerations. 



(a) Anabaena. Wlien purely vegetative filaiuents are exa- 

 mined microscopically, as already stated, an envclopiiig mem- 

 brane is readily evident only betwoen adjacont colls. Sporo- 

 irenons tilanients on tlie otlier band oxbibit well - niarked 

 lateral walls to the cells, which appear as a t'airly tbick 

 dark bne, wlien focussed so as to be seen in optica! section 

 (iig. 4 and ö). If sucb iibiments are stained witb an aqueons 

 Solution of lodine tbe following peculiar structnre appears (fig. 5). 

 The longitiidinal (lateral) walls of each cell are sbarply niarked 

 off from one another in adjacent cells (fig. 4, 5, c. s.) and appear 

 separated from one another by the colourless area, wbich repre- 

 sents the transverse wall between the two cells concerned (fig. 5, 

 t. s.). This latter is bounded laterally by a faint, slighlty con- 

 cave limit (cf. fig. 3b, t. s.). Carefnl examination reveals the 

 fact, that the free ends of the lateral walls are connected with 

 one another transversely by a very delicate line (1 in Fig. 5), 

 i'unning apparently right round each encl of the protoplast, the 

 transverse wall (t. s.) between adjacent cells, separating tlies(^ 

 lines from one another. In other words, looking at such stained 

 sporogenous filaments uncler a high ])ower, their appearance is 

 such as to give one the Impression that the lateral walls of 

 each cell form part of a hollow sheath-like cylinder around the 

 same, the open ends of whicli give rise to the above-mentioned 

 line, connecting the free ends of the lateral walls. Each cell of 

 the filament is thus surrounded by a special cylindrical sheath 

 of its own (=^ cell-sheath, fig. 5 and 8, c. s);, which, when divi- 

 sion of the cells takes place, is simply split into two fresh 

 sheaths by the develojDment of a colourless intercellular mass 

 (fig. 3a, b). When a cell of Anabaena is about to divido an 

 indentation of the lateral walls (= cell-sheath) appears at about 

 the middle of their length, giving rise to a constriction, running 

 round the middle of the mother-cell (fig. 3 a). At the same time 

 a very thin colourless strip (cf. fig. 3a, t. s.), appears in the cell- 

 contents on the same level as the constriction of the cell-wall 

 (cylindrical sheath) and, as this strip gradually increases in 

 width (fig. 3b) and develops into the intercellular colom^less area, 

 the new cells move apart from one another and the individual 

 cylindrical sheath of each becomes distinct. The details of this 

 process are difficult to observe and I am not at present pre- 

 pared to say, whether the Splitting of the sheath is a purely 

 physical process or whether it is the result of some special 

 structural change. In his recent preliminary paper on the cell- 

 structm-e of Cyaiwphyccac Wäger (04, p. 406) describes this 



