234 ARCHER, ON UESMIDIACE.E. 



in mind that the true generative process in Docidium Ehren- 

 bergii, like all other undoubted Desmidians, is by conjugation. 



Assuming that I am right, the bearing of the fact would 

 not be in the least to affect the acknowledged affinities of this 

 family with their more immediate allies, the Zygnemacese, or 

 with the Diatomacete ; for in the former, in Spirogyra and 

 Mougeotia, ciliated motile bodies, probably zoospores have 

 been noticed ; while in the Diatomaceae, although such a 

 phenomenon had been previously suspected, I need only 

 advert to the researches of the Rev. E. O'Meara (toe. cit.) } 

 which render it equally probable, if not decided, that such a 

 mode of propagation prevails also in that family. 



Such, then, is an account, deficient, as I regret it is, in 

 many points, of what I cannot but look upon, so far as I can 

 make out, as a new and unrecorded phase in the life-history 

 of this beautiful and interesting family, the Desmidiaceae, — a 

 life-history still obscure in many of its details, but yet one 

 which I aver will not yield in interest to any other portion in 

 the wide domain of our comprehensive science of Natural 

 History, and one also on which I shall deem myself very 

 fortunate and very happy should these humble observations 

 of mine, here recorded, ever be found eventually to shed even 

 a dim and solitary ray of light in its elucidation. 



Further Notes on Abnormal Growth in the Desmidiacea. 



In a former paper read to this Society (vide ' Nat. Hist. 

 Rev.,' vol. vi, page 469), I drew attention to an abnormal 

 mode of growth affecting several species of Desmidiaceae, and 

 I may add that I have since noticed similar cases in two or 

 three other species. This consisted in there being produced 

 between the old segments, not a pair of new ones eventually 

 to become symmetrical with the old, but an irregular, more 

 or less unsymmetrical inflated expansion, forming with the 

 old segments but one uninterrupted cavity ; and this kind of 

 monstrosity I endeavoured to show might probably be 

 primarily due to the omission of the formation of a septum as 

 a preliminary to ordinary vegetative growth. In PI. XI, 

 Fig. 7, I bring forward what seems to be a further extension 

 of the same identical condition of Arthrodesnws Incus, as that 

 figured in PI. xxxiii, Fig. 11, /. c. In the case last in- 

 dicated, as in the others, there must exist a Suture between 

 the older segments and the intermediate abnormal growth — 

 that is, the latter has become interposed between the older 

 segments by their separation at the original suture. 



