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. As a 

 rule the conjugation of Closterium is, in a sense, simple enough : two fronds 

 approach, join, open at a suture, and a zygospore is formed between them. 

 If, as in G. 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. selencewn. 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 Ealfs' 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, 1853, 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 G. 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 common mucous envelope, and not segregated in pairs as in C. 

 selenceum. 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 



