8 Vert Brecuer WITTROCK. 
opposite to each other, and in one species — P. Roettleri (Roth) nob, — 
partly even four in a whorl, has been mentioned before. 
If we try to give an account of the position the branches attached 
to different supporting cells have to each other, we find that it is 
mostly rather irregular. However, a tendency to a unilateral or bila- 
teral arrangement, at least for short spaces, is very evident in most 
species (pl. 1, fig. 7, 8, 13; pl. 2, fig. 3, 4, 7): 
The rhizoid part of the thallus is, in contrast to the cauloid, 
almost never ramified. Only m one specimen of P. kewensis nob. I 
have found a ramified rhizoid (pl. 4, fig. 8). Generally this part consists 
of only one vegetative cell (pl. 4, fig. 1, 4, 5, 15, 16, 17); —this is, at 
least, the rule in both the species, P. kewensis nob. and P. Cleveana 
nob., of which I have had a sufficiently rich material for examination, 
— but now and then rhizoids are found of an anomalous form. Thus 
it is not very rare in P. kewensis nob. to find rhizoids consisting of 
several vegetative cells (pl. 4, fig. 6, 7); and im the same species as 
well as in P. polymorpha nob. also I have found rhizoids, which have 
had, besides vegetative cells, as many as three spores, brought forth in 
the normal manner (pl. 4, fig. 9, 10, 11, 19). In contrast to this, speci- 
mens are sometimes found, in which the rhizoid is barely rudimentary. 
It consists then not even of a whole cell, but only of the very lowest 
part of the basal cell of the plant, which part has at the germination of 
the mother-spore taken its increase in an opposite direction to the 
cauloid (pl. 1, fig. 5, 8 rh; pl. 4, fig. 2, 3, 13, 14, rh). Im P. Cleveama 
nob. I have even found specimens, in which a rhizoid part has not at 
all been developed. Such a specimen I have represented pl. 4, fig. 12. 
(Compare the paragraph on »Germination and Increase.) 
It now remains, before I pass to treating the formation of spores, to 
account for the nature of the vegetative cells of the thallus. In sterile 
specimens, these are the only ones that occur; in fertile ones, spore-cells 
exist besides those. The vegetative cells agree with each ‘other in the 
following particulars: 1:0 They have the same principal form; they are 
all essentially cylindrical, even if some of them diverge from the cylindric . 
form in some one of their parts. 2:0 They have all a thin membrane 
of cellulose without layers. In Cladophoree particularly the cells belon- 
ging to the lower part of the thallus have often a thick membrane in 
distinct layers. 3:0 They all have a parietal body of protoplasm, forming 
a not very thick layer inside the cell-wall, and enclosing a great cylin- 
drical vacuole. — The thickness of the cells varies comparatively 
