22G ARCHER, ON DESM1 I) I A C K .E . 



gium in tlie Desmidiacese, it would seem that it is by a 

 repeated segmentation of the contents into a definite number 

 of portions, these becoming set free by the bursting of the 

 cell-wall of the sporangium, and eventually growing larger, 

 and, ordinary vegetable growth supervening, assuming the 

 characteristic form of the species, that the species is itself 

 perpetuated (Vide Hofmeister " On Reproduction in the 

 Desmidiae and Diatomese," translated in ' Annals of Natural 

 History/ January, 1858 ; also, De Bary, f Untersuchungen 

 iiber die Familie der Conjugaten, Zygnemeen und Desmi- 

 dieen/ taf. vi, figs. 12 — 24, and35 — 46) . Now it seems probable 

 that Morren's u large vesicles " were but the starch granules 

 common in these species, and that they were set free but by 

 the accidental fracture of the frond ; that his germinating 

 " propagules/' stated to produce the plant by gradual exten- 

 sion and growth, were most likely germinating sporangia, 

 after the contents had undergone segmentation into a number 

 of separate portions; that the fronds with unequal cones, 

 supposed by him to result from the unequal growth of the 

 sporangium, may have been merely detached and accidentally 

 unconjugated fronds, after having undergone self-division. It 

 is true that this explaining away of his statements leaves the 

 function of the active terminal granules in Closterium still 

 unexplained ; but I apprehend the true generative act in these 

 plants is to be sought, and is found, in the act of conjugation 

 itself. But, even admitting the correctness of Morren's ac- 

 count, and that there might be two modes of true generation 

 in these plants, still his " propagules" could hardly be looked 

 upon as zoospores, as these latter bodies, in what I believe 

 the strict and proper sense of the term, do not undergo fertili- 

 zation at all, and are ciliated and motile. I may remark, it is 

 possible the statements I have quoted from various works 

 may be based on Morren's account just alluded to, yet I do 

 not find references made to his memoir (written in 1X3(5). I 

 may add that Smith (I. c.) comes to the conclusion to which 

 1 had myself arrived, and which 1 ventured ere now to express 

 (' Nat. Hist. Review/ vol. v, p. 240), that the swarming 

 particles are not zoospores, and not connected with the 

 development of the species, and I am much pleased to find 

 my own previous ideas coinciding with those of so experienced 



an observer. 



There is only one other record which seems to hear at all 



on this point, at least which 1 have been able to gather, and 

 it is questionable whether it refer- here. I allude to Ehren- 

 berg's figure, given in his work 'Die [nfusionsthierchen/ 

 Plate ii, Pig. 15, where a Dumber of green zoospore-like bodies 



