40 



Veit Brecher 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 Pithoplioracece ; 

 it is, on the contrary, those propagative cells (of a somewhat accessorial 

 character) in Cladophorece, which I have before (page 18) mentioned as 

 ^prolific cells)). Knowing these cells best in onr common Cladophora fracta 

 (Dillw.) Kiitz., and having, moreover, the opportunity of referring the 

 reader to good representations of the prolific cells in this species, I 

 shall as a 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 Kutzing, Tab. Phyc, 

 part 4, plate 50, figs, h 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 Pithoplioracece. 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 Pithoplioracece. 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 Pithophoraceai are to be regarded as transformed Clado- 

 phorea;, thus being one of the branches on the stem of Confervacew. 



l ) 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 Pithoplioracece 

 and the prolific cells of Cladophorece. 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 Cladophorece do in germinating; see pi. 6, fig. (i, and the specific 

 description of P. oedogonia (Mont.) nob. 



