On the PiTHOPHORACEiE. 29 



species of Pithophora, spores which support branches (pi. 1, fig. 13, 16, 

 18 sp; pi. 2, fig. 2. 3, *13, 15 sp^ and others) '); but this does not de- 

 pend on a ramification from the spore cell, but on the fact, that the 

 original common mother cell of the branch and of the spore has first 

 formed a branch by cell-prolification ( = Abschnürung in the German 

 language) and afterwards, by the usual division into two, a spore in its upper 

 end (i. e. in that part of the cell, which supports the branch just for- 

 med). As exceptions, branches may be formed even from the subsporal 

 cells which are, as a rule, branchless. This is not seldom the case in 

 P. Zelleri (v. Mart.) nob. The vegetative cells are richer in protoplasm 

 in this species than in the others. The consequence of this is, in 

 general, that each cell, at least in the principal filament, forms not only 

 one, but as much as two spores. But sometimes the cells of the prin- 

 cipal filament form but one spore each, and then the not inconsiderable 

 quantity of protoplasm still remaining in the original mother cell is used 

 to form a normal branch, instead of a spore (pi. 1, fig. 9 hs). In the 

 other species of Pithophora I have observed a subsporal cell carrying 

 a branch only in one case, to vdt in the specimen of P. IceioenHis 

 nob. which I have represented pi. 2, fig. 7 (the subsporal branch is 

 marked bs). 



As we have seen by the exposition given above, a cauloïd and a 

 rhizoïd cell are formed simultaneously, in the germination of the spore. 

 But, whilst the first cauloïd cell gives origin by and by, by a continued 

 and in various ways modified division into two, to a great quantity of cells, 

 which form together a cauloïd of a comparatively complicated structure, 

 no further development takes place, as a rule, in the first rhizoïd cell. 

 A natural consequence of this is, that the rhizoïd part of the thallus 

 has a very simple structure; it is unicellular. Now and then it happens, 

 how.ever, particularly in P. keivensis nob., that the rhizoïd does not 

 remain in this low stage of development. In this case, the first rhizoïd 

 cell increases and divides into two in the same manner as the first cauloïd 

 cell, with the difference only, that the increase in the rhizoïd always 

 takes place in a different direction from that of the cauloïd. By this 

 increase the rhizoïd grows bicellular instead of unicellular (pi. 4, 

 fig. 11. Obs. A formation of spores, which has taken place later, has 



') Only in P. œqtialis nob. I have never found branches supported by spores. 

 Even the cells of the principal filament seem here .to lack the power of producing 

 more than one of these, a branch, or a spore (pi. 1, fig. 4, 5). 



