On THE PITHOPHORACEA. 23 
in length, and an upper one with the power of increasing apically in 
the longitudinal direction of the mother cell, and of bipartition. By in- 
crease and bipartition in accordance to the law now indicated, a single 
series of cylindrical cells is formed — the cells being longer or shorter 
according to the nature of the species and of the outer circumstances, — 
and this series of cells forms that part of the cauloid which I call, in 
its description, its principal filament. 
Only im very rare, exceptional cases the principal filament of the 
cauloid remains unbranched — perfectly branchless, full-grown specimens 
I have found now and then in P. equalis nob. (pl. 1, fig. 5) and P. 
Cleveana nob., and almost branchless in P. kewensis nob. (pl. 2, fig. 5). 
In common cases ramification takes place if not in all at least in most 
cells of the principal filament, and this very soon; generally long before 
the principal filament has attained its full development as to length. 
The oldest cells, — consequently those situated lowest, nearest to the 
mother spore of the specimen, — are the first which develop branches; 
aud afterwards the formation of branches proceeds from the lower and 
older cells to the upper and younger ones. —1. e. acropetally, — but 
not quite to the top cell, this being as a rule unbranched. 
The formation of the first cell in every branch takes place in the 
following manner. That cell of the principal filament from which the 
branch is to be formed, sends forth from one of its sides; a small space 
below the top, a small process, which is at first shaped like a truncated 
cone with a strongly rounded top, and which does not point straight 
outwards, but somewhat upwards (pl. 3, fig. 1 6). This process is formed 
by an increase as to the surface of the membrane, beginning round 
a central point, in consequence of which the membrane in this place by 
and by gets convex. Sometimes this increase of the surface takes place 
only in the inner layer of the membrane, which then, by its continued 
increase, breaks the outer layer (pl. 3, fig. 1 6) *); but sometimes the 
increase extends both to the inner and outer part of the membrane, and 
it is then not broken.”) As pl. 3, fig. 1 6 shows, and as is mentioned 
1) This circumstance strongly calls to mind the proceeding at the commencement 
of the formation of branches in the genus Bulbochete Ag. See Prinasu. Beitr. z. 
Morph. d. Alg. p. 22, pl. 2. 
2) | have not been able to distinguish, previously, two layers in a cell of a 
Pithophora ready for ramification, neither by optical nor by chemical means. Their 
existence, at least in some cases, is proved only by the circumstance mentioned 
above. 
