ARCHER ON CONJUGATION IN SI'IROTiKNIA. 147 



Although, then, this crude note possesses no value in assisting to 

 throw a further light on these problematic structures, yet perhaps it 

 may not be considered altogether without interest, for the following 

 three reasons: — (1), that their strictly parasitic nature in this instance 

 seems to be rendered very probable by reason of the destruction of the 

 Penium during their formation ; (2), as being the first instance (so far 

 as I am aware) of the occurrence of " Asteridia" in the Desmidiese ; and 

 (3), as being of a form and size not before noted in any of the various 

 " Asteridia" recorded (Fig. 4). So marked, indeed, in appearance are 

 the present examples, and looking at the same time upon " Asteridia" 

 in general as parasitic growths, the idea becomes suggested that there 

 may be distinct and constant forms amongst them, and that collectively 

 they ought to form a distinct genus. This suggestion I venture only to 

 throw out ; its confirmation or refutation will depend, of course, on time 

 and on a great number of independent observations. 



After which was likewise read the following paper : — 



On the Conjuoation of Spirot^nia condensata (Breb.), and of 

 Spirotjsnia truncata (Arch.). By "William Archer. 



The two minute unicellular algae which form the subject of the follow- 

 ing brief communication belong to a genus — Spirotaenia (Breb.) — com- 

 prising several well-marked forms. 



Most of these species are rare. In certain localities, however, the 

 first species now in question, Spirotcenia condensata (Breb.), is com- 

 mon ; the other, Spirotcenia truncata (mihi), belongs to the most rare, 

 having been, so far as I am aware, found only by myself, and that in 

 but one locality (" Feather-bed" Mountain). But it is not to be 

 understood, as regards Spirotcenia condensata, that any waters may pre- 

 sent this pretty species, for it must be sought for in suitable situations ; 

 then, indeed, it is frequently encountered. 



But often as S. condensata presents itself to notice, distributed, as 

 it appears to be, in Europe, and familiarised, as we cannot fail to be, 

 with this the commonest and at the same time the most beautiful re- 

 presentative of its genus, both it and its congeners have hitherto re- 

 solutely refused to reveal to us their mode of fructification or reproduc- 

 tion. Yet all the species are very constant to their characteristics, and 

 one could not resist the feeling, as regards them, unlike, perhaps, 

 many of the simple plants, that they must prove to be truly sui 

 generis. 



It is true, indeed, that d priori we would be justified in assuming 

 that the mode of reproduction in this genus, like that of Spirogyra, 

 &c, when found, would be seen to be by conjugation, and hence the 

 genus has been by most authors referred to the Desmidiaceee ; never- 

 theless, pending a knowledge of the actual process from direct obser- 

 vation, the true position of the genus has remained hitherto in doubt. 

 Thus, only the other day, in Eemsch's lately published work on ' The 



