330 TVes^ : Phytoplankton of English Lake District. 



casual or adventitious constituents, washed into the lakes by the 

 rains, and there either perishing very rapidly, or existing for a 

 more or less extended season. As stated before, it is our previous 

 detailed acquaintance with the general Alga-flora of the drainage 

 basins which has enabled us to clearly recognise the true 

 plankton-constituents from those which are casually introduced 

 by the drainage into the lakes. 



The following species and varieties are exclusively confined 

 to the plankton :■ — Micrasterias mahahuleshivarensis var. Wal- 

 lichii, M. radiata, Cosmarium abbreviatum var. planctonicum, 

 C. capitulum var. groenlandicum, Xanthidium antilopceum vars. 

 depauperatiim and triquetrum, X. stibhastiferum var. Murrayi, 

 Arthrodesmus crassus, A. triangularis var. subtriangularis, 

 Staurastrum curvatum, St. cuspidatum var. maximum, St. 

 jaculiferum, St. longispinum, St. lunatum var. planctonicum, 

 St. Ophiura, St. pseudopelagicum, Spondylosium pidchrum var. 

 planum, Ankistrodesmus Pfitzeri, Elakatothrix gelatinosa, Oocystis 

 lacitstris, SphcBrocystis Schrceteri, Tabellaria fenestrata var. 

 asterionelloides , Asterionella gracillima, Rhizosolenia morsa, 

 Anabcena Lemmermanni, Oscillatoria Agardhii, Gomphosphceria 

 lacustris, Microcystis ceruginosa, M. incerta, Mallomonas 

 longiseta, and Ceratium hirundinella. 



The following are much more abundant in the plankton 

 than elsewhere : — Euastrum verrucosum var. reductum, Micras- 

 terias Sol, Cosmarium depressum, C. subtumidum var. Klebsii, 

 Staurastrum anatinum and vars., St. Arctiscon, St. Brasiliense 

 var. Lundellii, St. denticidatum, St. furcigerum, St. paradoxum 

 var. longipes, St. sexangidare, Botryococcus Braunii, Cyclotella 

 compta, Melosira granulata, Fragilaria crotonensis, Asterionella 

 formosa, Surirella robusta var. splendida, S. biseriata, Lyngbya 

 bipunctata, Coelosphcerium Kiitzingianum, Microcystis pulverea, 

 and Peridinium Willei. 



It is particularly noticeable in the English Lake District 

 that a greater bulk of plankton occurs in those lakes which are 

 slightly contaminated by the presence on their shores of small 

 villages and farms than in those lakes free from contamination. 

 The greater bulk of plankton-organisms is most probably due 

 to the slight increase in the amount of food-constituents, 

 especially nitrates, consequent upon the slight sewage con- 

 tamination. 



We have no evidence in support of the view put forward 



Naturalist, 



