42 



Dansk Botanisk Arkiv, Bd. 3. Nr. 1. 



short horizontal filaments grow out which fuse together forming 

 the disc. 



From the cells in the disc gradually several erect ramified 

 filaments grow upwards forming a dense tuft (Fig. 39). 



The principal filaments consist in their lower part of short 

 cells about l^/g — 2 times as long as broad, their diameter reaching 

 a length of about 9 — 10 /i; upwards the filaments become gradu- 

 ally thinner and the cells at the same time longer. Near the 

 summit they are only about b fx thick and often upto 40^ long 



or more. Sometimes the cells in the lower part 

 of the principal filaments are a little broader 

 in the middle tapering towards both ends. 



The chromatophore (Fig. 40) is parietal 

 often with some longer prolongations along 

 the wall of the cell and contains a large pyre- 

 noid projecting somewhat into the interior of 

 the cell. 



The ramification of the filaments begins 

 near their base, but on the whole the filaments 

 are not much branched. Branches are given 

 off to all sides but often with long interwalls. 

 Two kind of branches are present, long fila- 

 ments like the principal ones and short branch- 

 lets upon which the sporangia are borne. 



The branchlets are as a rule one- or 

 two-celled ; in the first case it bears a single 

 terminal sporangium, in the latter the lower 

 cell also bears a mostly pedicellate, more rarely 

 sessile, sporangium. The last mentioned branch- 

 lets occur mostly in the lower part of the tufts, 

 while the first mentioned as a rule are only 

 present in the upper part. Only rarely are the sporangia seated 

 directly upon the main filaments. Branchlets with more than 

 two cells are rare. 



The sporangia (Fig. 40) are monosporous, oval-ovate, about 

 11// broad and about 14 — 16// long; they are provided with a 

 very thick wall, often up to 2/j. thick. 



This species seems at first sight to come near to Acrochætium 

 Hypneæ ; but it differs in a different arrangement of the spores, 

 these being sessile and seriated in Acr. Eypneæ; further Acr. 

 Hypneæ has endophytic filaments which I have not found in 



Fig. 40. Acrochæ- 

 tium robustum nov. 

 spec. Part of a fila- 

 ment with sporan- 

 gia-bearing branch- 

 lets. (About 700:1). 



