44 Verr Brecuer WirtTrocK.  - 
parag. 1, pages 6 and 7). The relative position of the branches also 
gives specific characters thus, that the branches are in some species 
regularly placed singly, in others two and two opposite to each other, 
and in others three or four in a whorl, partly at least (see above pages 
6 and 7). The existence or non-existence of so-called subsporal branches 
may also be used as a specific character.*) The same may be said of 
the helicoid cells; in one species, P. Cleveana nob., they are found in 
great quantity, in the others only very sparingly. That specific char- 
acters may be had also from the nature of the rhizoid, when a more 
complete knowledge of it is obtained, I think not improbable, although 
this part of the thallus, being in general rather rudimentary, seems to 
have a greater tendency to vary than the cauloid. 
The characters most essential in the distinguishing of species 
(and particularly of groups of species) are obtaimmed from the reprodue- 
tive system. In part of the species, viz. P. wqualis nob., P. oedogonia 
(Mont.) nob., P. Cleveana nob., P. kewensis nob.-and P. sumatrana 
(v. Mart.) nob. (that is, the american forms, the european one, and 
one of the asiatic), all the spores are (Gn each species) of the same 
principal shape, though differing as to length and thickness; thus, that 
the inclosed spores are all either cask-shaped or cylindrical, and the 
terminal are all either cask-shaped or cylindrical with the top pointed 
like a cone. But in the other species, viz. P. polymorpha nob., P. Zelleri 
(v. Mart.) nob. and P. Roettleri (Roth) nob. (all asiatic species) we find 
two or more forms, at least of inclosed spores. In P. polymorpha nob. for 
instance they are of three kinds, viz. some cylindrical, some cask-shaped 
and some of an irregular shape; whilst the terminal spores are of two 
kinds, viz. some cylindrical and some cask-shaped, in both cases with 
the top obtusely pointed and somewhat rounded. In P. Roettleri (Roth) 
nob. the case is analogous to that in P. polymorpha nob. In P. Zelleri 
(v. Mart.) nob. the inclosed spores are of three kinds, but the terminal 
are all alike. — It is on this peculiarity as to the spores, viz. that 
they are in some species of the same principal form, but show in the 
others different forms, that I have founded the two _ subdivisions, 
Pithophore isosporee and Pithophore heterosporee, in which the genus is 
divided. 
1) Besides in P. Zelleri (v. Mart.) nob. subsporal branches are also found at 
least in most specimens of P. oedogonia (Mont.) nob. (see pl. 6, figs. 4 and 5). 
