30 DUBLIN NATTJEAL HISTOEY SOCIETY. 



sporangia ultimately result from the two original fronds, conjugation 

 taking place between each of the opposite individualized pairs of par- 

 tially old, partially new, fronds— themselves resulting from the self-divi- 

 sion of the original parent fronds. A parallel phenomenon is furnished 

 in the process of conjugation by Closterium lineatum, as well as by se- 

 veral diatoms. Professor Smith was not able to see any further develop- 

 ment of the sporangium, and the propagules of Morren, he believed, had 

 no existence in fact. 



_ I believe the explanation of Morren' s statement to be possibly some- 

 thing like the following : —From researches of recent date in regard to 

 the after development of the sporangium in the Desmidiace®, it would 

 seem that it is by a repeated segmentation of the contents into a definite 

 number of portions, these by-and-by assuming the form of the parent 

 species mid becoming set free by the bursting of the cell- wall of the 

 sporangium, and eventually growing larger, that the species is itself 

 perpetuated (Vide Hofineister " On Eeproduction in the Desmidijfi and 

 Diatomese," translated in Annals of Natural History, January, 1858; 

 also, De Bary, ''Untersuchungen liber dieFamilie der Conjugaten, Z^^- 

 nemeen und Desmidieen," taf. vi., figs. 12-24, and 35-46). Now it 

 seems probable that Morren' s "large vesicles" are but the starch gra- 

 nules 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 extension and growth, were most 

 likely germinating sporangia, after the contents had undergone segmen- 

 tation into a number of separate portions ; that the fronds with unequal 

 cones, supposed by him to result from the unequal growth of the spo- 

 rangium, may have been merely detached and accidentally unconju'^ated 

 fronds, after having undergone self- division. It is true that this ex- 

 plaining away of his statements leaves the function of the active termi- 

 nal 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 fertilization 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 1836). I may add that 

 Smith {I. c.) comes to the conclusion to which I had myself arrived and 

 which I 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 these species, and I am much pleased to find 

 my own previous ideas coinciding with those of so experienced an ob- 

 server. 



There is only one other record which seems to bear at all on this 

 point at least which I have been able to gather, and it is questionable 

 whether it refers here. I allude to Ehrcnberg's figure, given in his work 



