ARCHER, ON DESMIDIACE.E. 



219 



just inference, not of direct proof, but of which indeed there 

 cannot be any reasonable doubt, it cannot always be insisted 

 on. But as to Pediastrum, I have before intimated that, so 

 far as I can see, the component cells do not increase in 

 number at all, and therefore in that respect cannot agree with 

 the terms of either diagnosis. 



The figured outline of the cells, often, however, confined to 

 the marginal series, yet wanting as they do bilateral symmetry, 

 seems then the reason why Pediastrum has been placed 

 amongst the Desrnidiacese. But, whilst arguing against the 

 claims of this genus, as such, I own I am myself unaware of 

 where else to place it. Its affinity with Hydrodictyon utricu- 

 Jatum seems sufficiently striking. That plant, with what, 

 however, must appear questionable propriety, has been 

 associated with the Siphonacese (' Micrographic Dictionary'), 

 a family of which Vaucheria may, perhaps, be assumed as 

 typical. Possibly Pediastrum and its allies, with Hydro- 

 dictyon, may prove a distinct family near Volvocinacese, with 

 which they seem perhaps connected through Pandorina and 

 Gonium, by certain points of similarity in their development, 

 or in which at least certain parallel phases seem noticeable. 



I had written so far of the present paper some months 

 back, and have read it as I then wrote it. Since then I have 

 met with Nageli's ' Gattungen einzelliger Algen,' also Al. 

 Braun's ( Algarum Unicellularium Genera nova et minus 

 cognita/ where I learn that the Adews of N'ageli and Braun 

 were identical with the conclusions that had forced themselves 

 on myself, and that those distinguished algologists had 

 actually long since seen fit to remove Pediastrum and its 

 allies from Desmidiacese, and have transferred them meantime 

 to the more humble family, Palmellaceae. 



While, then, the object of this paper is to prove that what I 

 think must be looked upon as zoospores do occur in at least one 

 species in this family, and, consequently, may occur through- 

 out, and that our books are therefore not wrong in assuming 

 it (leaving Pediastrum out of the question), still I am inclined 

 to think, as I before indicated, that the statements alluded to 

 are founded rather on the occurrence of what I am disposed 

 to imagine a distinct but, perhaps, more unaccountable phe- 

 nomenon, than on any published record of what, can be looked 

 upon as true zoospores, Pediastrum excepted. I allude to 

 what has been called the " swarming movement " of the ulti- 

 mate granules of the cell- contents, a phenomenon of common 

 occurrence in this family. Indeed, I believe I have myself 

 noticed it more or less frequently in nearly every species I 

 have seen, and even in those undergoing division. It seems 



