8 



Veit Brecher Wittrock. 



opposite to each other, and in one species — P. Roettleri (R'oth) 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 (pi. 1, fig. 7, 8, 13; pi. 2, fig. 3, 4, 7). 



The rhizoid part of the thallus is, in contrast to the caulo'id, 

 almost never ramified. Only in one specimen of P. kewensis nob. I 

 have found a ramified rhizoid (pi. 4, fig. 8). Generally this part consists 

 of only one vegetative cell (pi. 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 (pi. 4, fig. 6, 7); and in the same species as 

 well as in P. polymorph a nob. also I have found rhizoids, which have 

 had, besides vegetative cells, as many as three spores, brought forth in 

 the normal manner (pi. 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 (pi. 1, fig. 5, 8 rh; pi. 4, fig. 2, 3, 13, 14, rh). In P. Cleveana 

 nob. I have even found specimens, in which a rhizoid part has not at 

 all been developed. Such a specimen I have represented pi. 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: l:o 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:o They have all a thin membrane 

 of cellulose without layers. In Cladophorew particularly the cells belon- 

 ging to the lower part of the thallus have often a thick membrane in 

 distinct layers. 3:o 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 



