337 



in the full grown filaments about 2 4 times as long as broad : for 

 instance a filament was 50 JLI thick and the segments 150 ^ long. 



The dorsiventrality which is clearly expressed by the curved 

 summit of the plant and by the arrangement of the branchlets upon 

 the convex dorsal side of the filaments is also seen upon the trans- 

 verse section of the filaments, these having a more or less pronounced 

 bilateral appearance (Fig. 335 e g). The older parts of the plant 

 become, as mentio- 

 ned above, gradually 

 covered by a corti- 

 cal layer. In the 

 younger parts of the 

 filaments this does 

 not form any coher- 

 ent layer; in the 

 older parts, especial- 

 ly in the basal fila- 

 ments, it covers the 

 whole filament den- 

 sely. In spite of a 

 thorough search I 

 have not succeeded 

 in finding any young 

 stages showing the 

 development, but I 

 think we have to 

 do with a cortical 

 layer formed by hy- 

 phse. The fig. 336 c 

 shows the first sta- 

 ges found. At the 

 top on the left side of the figure a hypha has grown down from the 

 uppermost pericentral cell and, after having passed a segment, it 

 has grown together with the upper end of the pericentral cell of the 

 next segment being at the same time divided into two cells. On 

 the right side of the figure another hypha has grown down along 

 two segments and has been divided into 4 cells. 



It is much to be regretted that there was not found any kind of 



22 



Fig. 336. Cottoniella arcuata nov. spec, 

 a, 'summit of a filament seen from the dorsal side, 

 showing the zig-zag arrangement of the branchlets. 

 b, part of a decumbent filament with rhizoids. c, part 

 of a filament showing the development of the cor- 

 tical layer. 

 (a, about 350:1. 6, 80:1. c, 240:1). 



