On THE PlTIIOPHOEACEyE 



29 



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

 18 sj>; 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 ( = Abschnurung 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 bs). In the 

 other species of Pithophora I have observed a subsporal cell carrying 

 a branch only in one case, to wit in the specimen of P. kewensis 

 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 cauloid and a 

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

 But, whilst the first cauloid 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 cauloid of a comparatively complicated structure, 

 no further development takes place, as a rule, in the first rhizo'id cell. 

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

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

 however, particularly in P. hewensis nob., that the rhizoid does not 

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

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

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

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

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

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



') Only in P. cequalis nob. 1 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). 



