ostenfeld: the phytoplankton of victoria nyanza. 173 



this way in saying of the samples from April collected by Dr. Cunning- 

 ton (Z. c, p. 34-i) : " nur treten die Schizophyceen (Myxophyceen) in 

 diesem Fruhjahrs-Plankton zuriick." But it is not until we have the 

 still earlier samples collected by Dr. Agassiz that we may be justified in 

 drawing a conclusion concerning the seasonal change and its resemblance 

 to the seasonal changes of the "Baltic fresh-water plankton." 



Nevertheless, there are many differences between the plankton of Vic- 

 toria Nyanza and Lake Nyassa on the one hand and that of temperate 

 Europe on the other; e. y., it seems that the following dominant species 

 of temperate Europe, viz., Asterionella, Fragilaria crotonensis and Cera- 

 tium liirundinella, are wanting or, with regard to the last species, of 

 small importance in the large African lakes, while on the other side 

 those lakes contain a number of beautiful forms of Surirella and the 

 numerous Desmids. The last feature they have in common with the 

 lakes of West Europe (Great Britain), but the species are different. 



Tlie consecutive order of the plankton maxima in Victoria Nyanza is, 

 then, if we may be allowed to judge from our present very limited 

 knowledge, the following : — 



February (A. Agassiz ) : Melosira Agassizii dominates, other Diatoms 

 of less importance, Green and Blue-green Algae rather scarce. 



April (Cunnington) : Green Algae, both Desmids and Protoccoideae 

 dominate ; Diatoms of less importance ; Blue-green Algae i-ather scarce. 



October (Stuhlmann) and November (A. Borgert) : Myxophyccae 

 dominant, but both Green Algae (especially Botryococcus Braunii) and 

 Diatoms {Melosira nyassensis and Surirellae) subdominant. Plankton 

 very rich in species and individuals. 



From this fragmentary picture it will be evident how necessary and 

 important it would be to get a regular plankton investigation of Victoria 

 Nyanza throughout a year at least, and with short intervals (a week or 

 a fortnight). It is my hope that this gap in our knowledge of the fresh- 

 water plankton of the earth may soon be realized. 



2. The Samples from Mwanza and Shirati. 



The phytoplanktons present in the two February samples from Mwanza 

 and Shirati are not so abundant with regard to both species and individ- 

 uals as the organisms recorded from Victoria Nyanza samples taken 

 later in the year. 



The accompanying table will show the species found in the samples and, 

 further, their relative frequency given in the ordinary way, viz., cc de- 

 notes "dominant," c "common," -\- "not common nor rare," r "rare," 



