224 ARCHER, OX DESMIDIACE/K. 



tionary,' PL vi, Fig. 3 B ; also < Proc. Nat. Hist. Soc. Dub./ 

 1858-9, PI. i, Fig. 14 — irrespective, of course, of the external 

 abnormal condition). — The f Micrographic Dictionary' de- 

 scribes only the zoospores in Pediastrum as an a priori argu- 

 ment for their occurrence in the Desmidiacese generally, 

 assuming, erroneously, that genus as belonging to the 

 family. 



A recapitulation of this sort would, however, be incom- 

 plete without reference to a communication by M. Ch. Morren 

 in ' Annales des Sciences Naturelles,' torn, v, p. 266, 1836 — 

 1 Memoire sur les Closteriees.' In looking over the present 

 subject, I met with Professor Smith's paper on the " Conju- 

 gation of Closterium Ehrenbergii" (' Annals of Natural His- 

 tory,' second series, vol. v, p. 1), and therefore necessarily 

 with that by M. Morren alluded to ; and it seems to me impos- 

 sible not to coincide in the conclusions of the former on the 

 points in consideration, and consequently to look upon those of 

 the latter as founded in error. I shall endeavour briefly to state 

 the views of Morren, as founded on his observations on Closte- 

 rium Ehrenbergii. He believes that in the mature and merely 

 vegetating plant the endochrome is evenly distributed through- 

 out its entire cavity, and formed of extremely small granules 

 ("utricles"). By-and-by, however, there appears, towards 

 the middle of the frond, one or many darker longitudinal 

 regions, which soon become bands, subsequently changing 

 to be diaphanous, when the " utricles" become larger and 

 spherical, sometimes disposed in a single series, sometimes 

 in several, and these, he says, are nourished and increased in 

 size at the expense of the surrounding smaller granules. 

 These larger "vesicles" he now denominates " propagules," 

 and states they ultimately make their escape from the 

 parent frond by its dehiscence at the central suture, or are 

 protruded, along with the remainder of the endochrome, 

 en masse through a pair of apertures on the under side of the 

 frond. But further — he believes that the active granules 

 found at the extremities of this plant (as well, indeed, as in 

 all the species of Closterium, and in some Bpecies of 8 few 

 other genera), preparatory to the emission of his " pro- 

 pagules," leave their position at the extremity of the frond, 

 and, becoming mixed with them, exeri a fertilizing function 

 on the latter. The subsequent development of these "pi'o- 

 pagulcs" lie slates to consist in their gradual elongation from 

 their original Bpherical form; the endochrome, with the 

 gradual increase in size of the now young growing frond, be- 

 coming separated into two portions, the terminal spaces with 

 the active granules soon making their appearance as in the 



