ZOOLOGY A.ND BOTANY, MICEOSCOPY, ETC. 297 



material of this investigation was collected at various times by H. 

 Huitfeldt-Kaas from lakes in all parts of Southern N'orway. A short 

 account of each lake is given, with details of the samples taken and the 

 species they contained ; followed by a tabulated list of the species and 

 their frequency in the various lakes, as well as theii- presence or absence 

 in British and Danish lakes. After a systematic account of the more 

 interesting species, the author gives a summary of the conclusions 

 resulting from the investigation. The Desmidiace^ are among the 

 very few fresh-water algte that have a really geographical distribution, 

 owing to the fact that they soon perish by desiccation in a vegetative 

 state, and they rarely produce zygotes. Geographical communities of 

 Desmids already differentiated are Caledonian, Indo-Malayan, Australian 

 and Arctic. Barriers are probably formed more efficiently by large 

 tracts of unfavourable localities than even by the oceans. The 

 Desmidiaceffi that have the most distinctive geographical distribution 

 are chiefly those that make the greatest claims on the pliysical resources 

 of the growing-places. The author considers that absence of lime is 

 the main condition on which the occurrence of Desmids depends, which 

 confirms the view held by Messrs. W. and G. S. West. The replenish- 

 ment of the Desmid flora in lakes is provided by the washing down of 

 benthos species from surrounding bogs, and those species that have 

 been most fit for the pelagic life have flourished and propagated there, 

 and developed into new species of plankton. Examples are given of 

 the process, which is in course of evolution. Three groups of plankton 

 Desmids are characterized as follows : — (1) Desmidiacete belonging to 

 the microphytic benthos, washed off into the plankton accidentally but 

 not propagating there; (2) Desmidiaceaj originating from the micro- 

 phytic benthos, but propagating under the pelagic conditions of life ; 

 (8) varieties or species only occurring in the plankton, specified by 

 Messrs. West as (Pv) and (P), in their " British Freshwater Phyto- 

 plankton,'-' 1909. 



At present only one plankton formation can be clearly defined — 

 namely, the Caledonian — and this is frequently found in lakes in 

 Sweden, jSTorway up to71 N. Lat., the Faroes, Iceland, the British 

 Isles, etc. The Danish plankton has, on the other hand, a typical 

 Baltic character. The Desmidiacete constitute about one-half of the 

 plankton species and varieties in the lakes discussed in the present 

 paper. E. S. Gepp. 



Phytoplankton from Lake Wig-ry near Suwalki in Poland.— 

 B. Schroder {Ber. DeutscJi. Bot. GeselL, 1917, 35, :^56-66 ; see also 

 Bot. Gentralbl, 1918, 138, 294). Material collected on Aug. 24, 1917, 

 contained a considerable quantity of Anabaena Jios-aquse, and a still 

 larger proportion of Microcystis seruginosa, Characium de baryanum, 

 Ceratium hiruncUneUa, Fragilaria krotonmsis, Eudorina eUgans, and 

 Spliserocgstis schroterL On the other hand, many species characteristic 

 of Baltic lakes were lacking. Possibly they occurred at other times of 

 the year. Ceratium hirundindla was present in three forms : with two 

 ant-apical horns: with two normal and a third rudimentary; and with 

 three normal ant-apical. The preponderating form in the Wigry lake 



