414 
The erect filaments are very slowly attenuated upwards; at the base they are 135 
— 160 w thick. 
The upper end of the shoots has the same aspect as in P. violacea. Each joint 
bears a trichoblast except the undermost 3 or 4 (or 5) of the branches. The tricho- 
blasts, which remain rather long, have the usual appearance; their cells contain 
one nucleus only. The branches arise as axillary buds of the trichoblasts; they are 
separated by 4 or 5 trichoblasts without branches, but two branches frequently 
follow one another. Secondary axillary shoots do not occur, or only appear excep- 
tionally on the lower rhizoid-bearing joints. The first trichoblast of the branches 
appears on the 4th, 5th or 6th joint. Endogenous branches may occur in the pro- 
cumbent filaments and in the lower part of 
the erect ones. 
The tetraspore-bearing shoots have the 
same structure as in P. violacea. The joints 
N have 6 pericentral cells and, under one of 
them, a short peripheral cell situated to the 
right of the basal cell of the trichoblast of 
the foregoing joint (fig. 352). 
The antheridia are unknown. 
Fig. 354. The cystocarps are subglobose or slightly 
Polysiphonia Rhunensis Thuret, from St. Vaast (herb. depressed (fig. 353). The ostiole is not pro- 
Thuret), an unripe, and a ripe cystocarp. 107:1. tracted, it is situated on the apex of the 
cystocarp opposite to the point of insertion, 
not on its ventral side as in P. violacea and in P. Rhunensis, of which I have examined 
an original specimen from THURET collected at St. Vaast (fig. 354). The series of 
cells forming the outer layer of the wall run in the same direction as the stipe, and 
the placenta is perpendicular on this direction (fig. 353), while in P. Rhunensis the 
cell-rows run towards the ventral side and the placenta has an oblique position to 
the stipe. In the latter species the ostiole is moreover a little protracted and, according 
to THURET (1. c. p. 85), often a little sinuous. The cells surrounding the ostiole in 
P. orthocarpa are low, not prominent. , 
The specimens from the Limfjord resemble P. Rhunensis so much that I have 
been inclined to consider them as belonging to the same species. They agree with 
it by the cespitose growth, numerous erect filaments issuing from a system of creep- 
ing filaments, by the want of cortication, further, as substantiated by examining 
original specimens of THURET's, by the branches arising in the axils of the tricho- 
blasts and by the want of secondary axillary branches. Our species differs, however, 
from THURET's species by the erect filaments being thinner at the base (1/4 mm in 
P. rhunensis) and less tapering upwards, by the presence of rhizoids from the erect 
filaments and by the apical, not protracted ostiole of the cystocarps. By the shape 
of the cystocarp it is also distinct from P. violacea, in which the ostiole has a more 
or less ventral position and is surrounded by a prominent border composed of rather 
large projecting cells. 
