152 NATURAL HISTORY SOCIETY OF DUBLIN. 



As regards- the plant itself in the unconjugated state, I might men- 

 tion that the cells seemed to be somewhat more minute than when I 

 saw it on the first occasion ; also the spiral band was rather more 

 narrow and definitely margined, and sometimes appeared to branch or 

 subdivide, and the enveloping gelatinous envelope was less marked. 

 The latter circumstances might, perhaps, be accounted for, as in S. 

 condensata, by the gathering in which they were detected being for 

 some time in the house. But though the spiral band was more sharply 

 defined, and any scattered granules likely to impede the view into the 

 interior of the cavity of the cell were likewise fewer than when I pre- 

 viously had seen this species, I was yet unable to perceive a nucleus 

 satisfactorily. The narrow truncate extremities and the characteristic 

 little space in each, now with one quiescent darkish granule, were there 

 as before, which, combined with the solitary band of endochrome and the 

 cylindrical figure, tapering towards the ends, rendered it without 

 doubt one and the same plant. I was much pleased, therefore, to 

 find this very distinct species a second time after so long an interval, 

 especially in the conjugated state, forming, indeed, the second known 

 instance of conjugation in the genus. 



I have alluded to the recent work of Reinsch, in which he denies 

 to " Palmogloea macrococca" (Kiitz.) — more properly, surely, regarded 

 as a species of Mesotsenium — a place amongst Desmidiaceee, and this 

 because he believes the plan of conjugation in that plant to hold a 

 middle place between that of a typical Desmidian and the Zygnemacese. 

 He holds that each parent-membrane of the conjugating cells of Meso- 

 tsenium (which, notwithstanding the heterogeneous and incongruous 

 character of Kiitzing's genus Palmogloea, he still is inclined to refer 

 thereto) actually takes a share in the formation of the zygospore itself — 

 nay, even that the two coalesce so as to form its special membrane, and 

 that hence it cannot be placed with Desmidiacese on the one hand, nor 

 with Zygnemacese on the other. At least, then, a place in the Desmi- 

 diaceae could not be refused to Spirotcenia condensata nor to 8. truncata 

 on the same grounds. Here, manifestly, the parent-membranes take 

 no share in the formation of the zygospore — not even so much as to 

 form a connecting canal, as in Spirogyra or Zygnemaceee generally. 

 But, though it may be in a measure apart from the subject proper of 

 this communication, I cannot refrain from expressing my conviction 

 that Eeinsch is in error in the view he expresses as regards the process 

 of conjugation in Mesotsenium {Palmogloea macrococca, Kiitz.). I ven- 

 ture to say that here the membranes of the parent-cells do not take a 

 part in the formation of the zygospore, but that during the conjugation 

 they aregradually thrown off, and probably become dissolved, and help so 

 to increase the surrounding gelatinous matter. They, in fact, come 

 away, leaving the contents to become mutually fused, quite as they do 

 in Penium or in Cylindrocystis, &c, only they are more fugitive. See on 

 this point de Bary's figures* in Mesotsenium as well as Cylindrocystis, 



* " Untersuchungen," &c, t. vii. ; also my own communication, " Proceedings of the 

 Natural History Society of Dublin," vol. iv., p. 12, PI. I.,. Figs. 8-14, Mesotsenium, and 



