239 — 



and J. Holmboe 1 ) contain a few scattered notes on the plankton- 

 organisms; but a general treatment of the plankton-flora of one or 

 several lakes has not yet been published. In Wi lie's last paper, 

 and in the paper by Holmboe most of the plant-organisms found 

 in Harsjön and in Lomnæssjon have been recorded from Norway, 

 but there are a few more which may be added to the list and 

 which I shall enumerate below together with notes on some of the 

 forms already recorded. 



Notes on some of the forms found in the samples. 



I. CMorophyceæ. 



Sphærocystis Schroeteri Ghodat. This peculiar Palmellacea occurred 

 in great numbers in both samples from Harsjön. The greater part of 

 the different stages figured by Ghodat (Algues vertes de la Suisse, Bern, 

 1902, figs. 50 and 53) have been observed. 



Chlamydomonas sp.(?). On the surface of the mucilage of Sphæro- 

 cystis a small green alga was often found; it consists of a few or several 

 small isodiametrical cells, lying closely together, so that their cell-walls 

 become a little polygonal ; their diameter is about 5 fi , and they contain 

 starch. As 1 had only preserved material for examination, I have not 

 been able to determine this alga, but the layers have a great resemblance 

 to the „ états larvaires" of Chlamydornonas Reinhardi which Ghodat (I.e.) 

 has shown in figs. 54, j — l and 55, m — n. Perhaps they belong to the 

 same alga of which I found the resting-cells, and which I have called 

 Trochiscia sp. in the table. Professor Wille' 2 ) has lately pointed out 

 that the Trochiscia probably is the resting-stage of Chlamydomonas. 



Crucigenia rectangularis (A. Br.) Ghodat. In the sample from Harsjön 

 of the 8 th of August 1899 this alga was rather common in its typical form, 

 like Chodat's fig. 126 (I.e.). But in the sample of the 17 th of July 1900 

 I saw one colony only, and it contained many and more irregular cells 



1 ) Holmboe, J.: Undersøgelser over Norges Ferskvandsdiatomeer, I. Diatoméer 

 fra Indsjøer i det sydlige Norge. Archiv for Mathematik og Naturvidenskab 

 XXI, Nr. 8, 1899. 



2 ) Wille, N. : Studien über Chlorophyceen, Christiania Vidensk. Selsk. Skrifter 

 1900, Nr. 6, Christiania 1901, p. 12. 



16* 



