36 DUBLIN NATTJEAL HISTORY SOCIETY. 



but I cannot doubt it. Wben I made this particular gathering, I did 

 not meet the Closterium so affected in numbers sufficient to make any 

 definite observations ; but I suppose the plants must have given birth 

 to, and emitted their contents in the form of the gonidia lying about. 

 For certainlj", the bodies scattered around did not occur anywhere else, 

 but always in the neighbourhood of a Closterium contaiaing these or- 

 ganisms ; and where they nearly all, or a few only, still contained their 

 endochrome, these abounded close by in the relative numbers to be ex- 

 pected. Admitting them to be such, it may appear questionable whether 

 this growth be connected with the development of the Closterium itself, 

 or whether it be a true parasite. I am disposed myself to think the 

 latter. But, be this as it may, I need hardly insist on the essential dis- 

 tinctness between the phenomenon depicted in Fig. 5, and the condition 

 of Docidium shown in Figs. 1 to 4. It may be well to say that the 

 three ovate ciliated bodies on the Plate near Fig. 4 represent the zoo- 

 spores appertaining to it, whereas all the other scattered orbicular bodies 

 belong to Fig. 5. ^Notwithstanding any description I can offer is so 

 very incomplete, I venture to tliink the drawing itself (a faithful copy 

 from nature), may prove interesting. It seems highly probable that 

 Ehrenberg's genus Polysolenia, included by him and by Kutzing in Des- 

 midiacse (vide Kiitzing, " Species Algarum"), must have been truly a 

 Closterium (probably C. didymotocum) so attacked. I draw attention 

 here to this very interesting growth, in order to guard against any pos- 

 sibility of its being thought the remarkable condition of Docidium is 

 identical with it, or that 1 may have myself in any way mistaken the 

 one for the other. 



Here, however, my observations conclude, for I am totally unaware 

 of the after development of the motile gonidia, the original formation and 

 emission of which I have described. It may be urged that I cannot prove 

 these bodies to be truly zoospores, because I cannot prove they grow into 

 young Docidia, as can more or less readily be done according to the spe- 

 cies in various other Algae, in which the growth of the zoospores into 

 young plants similar to the parent is witnessed with not great difiiculty. 

 Possibly the bodies I have described may be but equivalent to those de- 

 scribed in some algae as microgonidia by the German writers ; but I can- 

 not for the present see the probability of this assumption, and imagine 

 they are more likely to be true motile buds or zoospores. It will be 

 borne in mind that the true generative process in Docidium Wirenhergii, 

 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 Zygnemaceae, or with the Diatomaceae ; for in 

 the former, in Spirogyi-a 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 Qoc. cit.), which render it equally 

 probable, if not decided, that such a mode of propagation prevails also in 

 that family. 



