256 - Transactions.— Botany. 
Mr. Smith (loc. cit.) says that Closterium ehrenbergii stands alone amongst 
the European Closteria in producing double zygospores. It is, therefore, 
not uninteresting to have to add to it in this respect a plant from New 
Zealand. But I have some doubt whether Mr. Smith's statement is alto- 
gether correct, in view of a noticeable feature in the conjugation of the 
next plant on my list, which affords, I think, foundation for a closer study 
of the phenomenon in connection with other plants of the genus. Asa 
rule the conjugation of Closteriwm is, in a sense, simple enough : two fronds 
approach, join, open at a suture, and a zygospore is formed between them. 
If, as in C. rostratum, the fronds open at the median suture, the segments 
attached to the zygospore will be equal in length: should there be secondary 
sutures as in C. intermedium, the fronds may open at these and the segments 
will be unequal, but the inequality will be easily intelligible. In the case of 
C. acerosum, Schrank, 
Fig, 18. 
the process, to a certain extent, resembles that in C. selengum. That 
is to say, the segments attached to the zygospore are unequal, although 
there are no secondary sutures. The inequality is shown in my figure 18 b, 
where each frond has one long arm and one very short one. This inequality 
is also shown in Ralfs’ plate xxvii, but no reference is made to it in the 
text. Mr. Archer, in Pritchard's * Infusoria," likewise says nothing of it, 
Von Siebold, in the Journal of the Micros. Society, 1858, seems to refer to 
something of the kind, though I do not understand his expression: he 
speaks of “ only the two upper and lower halves " coalescing, a phrase 
which may mean anything. 
In the spring of last year I gathered on one occasion a small quantity 
of C, acerosum in conjugation. Although unable to watch the process from 
its commencement, I examined the gathering with great care. There must 
have been several hundreds of plants in it, and they were all surrounded 
with a eommon mucous envelope, and not segregated in pairs as in C. 
selengum, When the mass was first placed on the slide many of the fronds 
were already in full conjugation, and many others had completed the pro- . 
cess. A small proportion (less than one in ten), presented the normal 
form of the plant, with two equal arms, as in my figure 18 a, the uppermost 
figure. A few more appeared as the second shown in fig. 18 a, and the 
rest had still shorter arms, the greater number of all being as in my lowest 
figure, with one arm almost an equilateral triangle. Conjugation invariably 
occurred between two fronds of this last form, never in any of the others. 
If, in the conjugating fronds, I had detected any folds or wrinkles in the 
cell-wall of the shorter arms, I could have concluded that in the process 
that arm, for some reason or other, shrank up. But no such folds were 
