696 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Reproduction of Stigeoclonium.* — A. Pascher describes phenomena 

 connected with the reproduction of a species of Stigeoclonium, which is 

 probably S. nudiascuhim. In calm water there was observed a rich 

 formation of hairs. By transferring material from disturbed to calm 

 water, the author was able to bring about in every case the formation of 

 swarm-spores. The reproductive bodies were either macrospores or 

 microspores, which either became resting-spores, or formed zygotes, or 

 were transmuted into aplanospores. Zoospores with two cilia and 

 akineta3 stages, as well as the Palmella condition, seemed to be entirely 

 wanting. From an examination of other species, the author finds that 

 morphologically similar species of Stigeoclonium do not by any means 

 always show similar forms of reproduction, or the same behaviour of the 

 swarm-spores. Details of the spores, size, etc., are given of the material, 

 regarded by the author as either S. tenue or S. falklandicum, on which 

 some of his conclusions are based. Copulation was several times 

 observed between the microspores. 



Icelandic Plankton.j — 0. H. Ostenfeld and C. Wesenberg-Lund 

 publish an account of the plankton of two lakes — Thingvallavatn and 

 Myvatn, iu the south-west and north of Iceland respectively. The 

 phytoplankton has been worked out by Ostenfeld, and the zooplankton 

 by Wesenberg-Lund. In Myvatn, no phytoplankton was found at all, 

 and in Thingvallavatn there were no plankton Myxophycea?, and indeed 

 the main interest of the algal collections lies in the non-occurrence of 

 forms which one would have expected to find. The Diatoms constitute 

 the main part of the species, and the commonest of these are the Melo- 

 sirse and Aster ionella formosa. Fragilaria crotensis occurs very sparingly 

 and only at the highest temperatures. The limnetic Chlorophycese are 

 not abundant, and C&ratium hi/rundinella and Dinobryon are absent. 

 Since the samples were collected regularly every fortnight during a 

 whole year, the authors are able to draw conclusions of great value from 

 the results of their examination. They think it probable that the 

 plankton of the arctic lakes consists mainly of zooplankton, to a much 

 greater degree than is the case with that of more southern countries ; 

 also that the phytoplankton, especially in summer time, only plays an 

 insignificant part. In arctic and sub-arctic lakes it consists in all prob- 

 ability of alga3 with yellowish or yellowish-brown chromatophores ; alga? 

 with green or blue-green chromatophores being almost entirely wanting. 

 As exceptions to this rule may be mentioned Sphcerocystis, the semi- 

 limnetic Desmids, and a few rare Chlorophycese. The authors conclude 

 their interesting paper by remarks on W. and G. S. West's " Freshwater 

 plankton of the Scottish Lochs."| A list of literature is followed by 

 two plates and a photograph of Thingvallavatn. 



G-riffithsia acuta Zan.§ — G. B. de Toni has made a study of this 

 alga, which was never described by its author, and the original specimen 

 of which is preserved with the rest of Zanardini's herbarium in the 



* Archiv Hydrobiol. u Planktonk., i. (1906) pp. 433-8. 



t Proc. Roy. Soc. Edinburgh, xxv. (1906) pp. 1092-1197 (3 pis., figs, in text). 



% Trans. Roy. Soc. Edinburgh, 1905, p. 477. 



§ Comptes Rendus Assoc. Francaise pour l'Avancement d. Sci., 1905, pp. 402-5. 



