1908.] 



The British Freshivater Phytoplankton. 



167 



have been worked very extensively, and as we did not begin plankton 

 investigations until 1900, we have a much more complete knowledge of the 

 general Algse-flora of these areas — such as is found in the bogs, lake-margins, 

 streams, on the wet rocks of the glens, etc. — than of the phytoplankton, In 

 consequence of this previous detailed acquaintance with the Algee of the 

 lake-areas, we are enabled with a considerable degree of accuracy to state 

 which species should be considered as true constituents of the plankton and 

 which should not. The other constituents are casual or adventitious, and 

 their sojourn in the plankton is both temporary and accidental. 



The work has been entirely of a qualitative character. We have had 

 neither the time nor the necessary funds to conduct quantitative investiga- 

 tions such as those carried out by Apstein,* Zacharias,f Lemmermann,j 

 Volk,§ etc., in Germany, by Wesenberg-Lund|| in Denmark, by Huitfeldt- 

 KaasIT in Norway, and by others in Switzerland and the United States.** 



We have also met with many difficulties in attempting to acquire a 

 knowledge of the periodicity of the plankton of the British lake-areas. 

 Neither academic duties nor funds have permitted the necessary number of 

 visits to these areas which would be required in the course of a year in 

 order to obtain an adequate idea of the periodicity of the plankton. At the 

 very least, monthly visits would be imperative for reliable results to be 

 obtained ; and to collect material from a number of lakes, even in one 

 district, would require several days, not to mention the difficulty, and in 

 some cases the impossibility, of obtaining boats in the winter months. It is 

 likewise no easy matter to find suitable men on the spot of sufficient 

 intelligence to carry out detailed instructions at regular monthly intervals 

 throughout the year.ff 



* Apstein, ' Das Siisswasserplankton, Methode und Resultate der quantitativ. Unter- 

 suchung.,' Kiel und Leipzig, 1896. 



t Zacharias in ' Forschungsber. Biol. Stat. Plon,' vol. 3, 1895, etc. 



I Lemmermann, "Das Plankton der Weser bei Bremen," 'Archiv fur Hydrobiologie 

 und Planktonkunde,' Bd. 2, 1907. 



§ Volk, " Hamburgische Elbe-Untersucliung., I u. VIII," ' Mitteilungen aus dem 

 Naturhist. Mus. Hamburg,' Bd. 19, 1903 ; Bd. 23, 1906. 



|| Wesenberg-Lund, ' Studier over de Danske Soers Plankton, Kjobenhavn,' 1904. 

 IT Huitf eldt-Kaas, ' Plank tonundersogelser i Norske Vande,' Christiania, 1906. 

 ** C. Dwight Marsh, in ' Wisconsin Geol. and Nat. Hist. Survey Bull.,' No. XII, 1903 ; 

 Kofoid, in 'Bull. Illinois State Laboratory of Nat. Hist.,' vol. 8, 1908. 



tt We are at present receiving regular periodic collections, with *ome necessary data, 

 from several of the Scottish lochs and from some of the lakes of the English Lake 

 District. We have been able to arrange for these collections by means of a further grant 

 from the Royal Society. Periodic collections have also been made for a period of two 

 years from one of the large pools of the Midlands. The details of all these collections 

 will be published shortly. 



N 2 



