1106 Proceedings of Royal Society of Edinburgh. [sess. 
( b ) Phytoplankton. By C. H. Ostenfeld. 
1. General Remarks. 
Last year Dr Wesenberg-Lund asked me to examine the plant- 
organisms in a series of samples from Thingvallavatn. I was 
very pleased at his request, as I just had published a little note on 
a plankton sample from an Icelandic lake, as well as some smaller 
papers on fresh- water phytoplankton from the Faeroes and from 
Norway. But the samples from Thingvallavatn were of special 
interest, because they were collected regularly every fortnight 
during a whole year, thus giving an idea of the seasonal changes 
in the plankton of a lake in Iceland. I therefore took up the 
work with pleasure. Very little is known concerning the phyto- 
plankton of the northern countries ; in the arctic region we have 
small contributions from Greenland (E. Vanhoffen, 1897) and Bear 
Isle (G. Lagerheim, 1900); to these we must add contributions 
from the Lule Lappmark (Miss A. Cleve, 1899) and from the 
Murman coast of Finland (K. M. Levander, 1901). There are 
further published some papers on the phytoplankton of Swedish 
lakes (0. Borge, 1900 ; Lemmermann, 1904 a), but very little from 
Norway (Holmboe, 1900; Ostenfeld, 1903). From the United 
Kingdom we have publications from Ireland and Scotland (W. and 
G. S. West, 1902, 1903 ; O. Borge, 1897), and small notes from the 
river Thames (F. E. Fritsch, 1902, 1905) ; an examination of phyto- 
plankton from the Faeroes has also been published (F. Borgesen 
and Ostenfeld, 1902), as well as one of a single sample from a lake 
in South Iceland (Ostenfeld, 1904). All these publications have in 
common the drawback that they are based upon samples which 
have been collected only in the summer time and without any 
regularity. It is only in Denmark (Wesenberg-Lund), Germany 
(O. Zacharias, Lemmermann, etc.), Switzerland (C. Schroeter, R. 
Chodat, H. Bachmann, etc.) ; United States (Illinois, by C. S. Kofoid, 
etc.), and partly Hungary and Russia, that more regular investi- 
gations have taken place. The task undertaken by Dr Wesenberg- 
Lund — to obtain a series of samples from lakes in Iceland collected 
during an entire year — is therefore a very interesting one. 
