4() Veit Brecuer WITTROCK. 
consist of zoospores. But it is not these that seem to me to offer points 
of comparison in the explanation of the spore formation in Pithophoracea; 
it is, on the contrary, those propagative cells (of a somewhat accessorial 
character) in Cladophorew, which I have before (page 18) mentioned as 
»prolific cells». Knowing these cells best in our common Cladophora fracta 
(Dillw.) Kiitz., and having, moreover, the opportunity of referring the 
reader to good representations of the prolific cells m this species, I 
shall asa matter of course fix my attention principally on the nature of 
this Cladophora. The prolific cells of C. fracta (Dillw.) Kiitz. can, as has 
been said before (page 18), assume several different shapes. One of 
the most common is the shape of a pear; see Ktrzine, Tab. Phyc., 
part 4, plate 50, figs. 6 and d. This shape of the prolific cell has its 
cause in the widening of the upper part of the cell (which was cylin- 
drical before), whilst the lower part retains its original shape and thick- 
ness. At the same time the upper, widened part is also filled with 
richer chlorophyllaceous contents than the lower. Thus we here see 
two acts in the formation of prolific cells, which take place likewise in 
the formation of the hypnospores in Pithophoracew. If a division were 
made of the cell thus transformed, by the formation of a transversal 
cell-wall just below the widened part, two cells would be obtained, of 
which the upper one would be perfectly analogous to the spore, and the 
lower to the subsporal cell, in Pithophoracea. If the formation of zoospores 
ceased at the same time, which would not seem impossible, because the 
cell-contents had been disposed of for other purposes, a Cladophora 
would have been changed into an almost perfect Pithophora. That this, 
or something like it, has taken place in the realm of nature, seems to 
me not improbable; *) and on this supposition, as well as in the first 
place on the evident conformity of the vegetative system, I found my 
opinion that the Pithophoracew are to be regarded as transformed Clado- 
phoreew, thus being one of the branches on the stem of Confervacee. 
1) In Pithophora oedogonia (Mont.) nob. I have later had the opportunity of 
making an observation which seems to me to give a very powerful support to the 
opinion pronounced above on the relationship between the spores of Pithophoracee 
and the prolific cells of Cladophoree. In the species of Pithophora now mentioned it 
not rarely happens, that real spores, formed in the normal manner, instead of germi- 
nating in the usual way, develop a branch laterally, quite in the same manner as 
prolific cells in Cladophoree do in germinating; see pl. 6, fig. 6, and the specific 
description of P. oedogonia (Mont.) nob. . 
