86 DR. С. S. WEST ON THE ALGÆ OF 
П. PFeb.—July (warm period or summer phase).—Desmids dominant. 
Melosira granulata and Cocconeis Placentula conspicuous. 
ИГ. ере. Осі. (cold period).— Very little Algal life, at any rate in the 
active Vegetative condition. Tabellaria floceulosa and Van- 
heurckia viridula both noticeable. 
о 
3. Some light is thrown on е ORIGIN OF THE MICROPHYTIC BENTHOS AND 
OF THE PHYTOPLANKTON by the investigations carried out in other parts of the 
drainage area. The upper dams (Toorourong Reservoir, Wallaby Creek 
Weir, and Silver Creek Weir) yield few plankton species owing to the disturbed 
state of the water, but their examination indicates that the Yan Yean Reservoir 
does not derive its numerous Algal constituents from these dams although receiving 
siw-sevenths of its water-supply from them. The rich Alga-flora of the Yan 
Yean appears to be derived almost entirely from its own small catchment basin, 
and along the two marshy inlets of Rana Creek and Ottelia Creek. 
The phytoplankton is partially recruited from the microphytic benthos, and it 
also consists in part of well-established forms which are not recruited from the 
shore-regions. Some of these well-established plankton forms seemingly supply 
the benthos with recruits in greater or smaller numbers during the autumnal fall 
of temperature. 
Some of the plankton species are not derived from the benthos, and neither 
do they appear to be acquired by the aqueduct which brings the chief water- 
supply from the large drainage area. Аз these species are in some cases 
dominant forms, they must have been established in the plankton for some 
time. Their actual origin is mostly a matter for future investigation. 
4. Over 300 species of Algw were observed in the complete collections from 
the entire Yan Yean drainage area. Of these, 14 species and 11 varieties ате 
here described for the first time, and 4 species and 5 varieties which had 
previously been only partially described are here dealt with in greater detail, 
and for the first time figured. 
University Botanical Laboratory, Birmingham, 
April 1908. 
EXPLANATION OF THE PLATES. 
PLATE 1. 
Photomicrographs of plankton from the Yan Yean Reservoir. Two upper photographs 
January and March ; two lower photographs April. All x 100. 
Figs. 1 & 2, Pediastrum duplex var. reticulatum; З. Scenedesmus bijugatus forma arcuata ; 
4 & 5. Melosira granulata; 6. Tabellaria flocculosa ; 7 E 8. Dinobryon cylindricum 
var. divergens; 9. D. elongatum var. undulatum. 
10. Micrasterias Hardyi; 11. Staurastrum leptacanthum ; 12 & 13. 5. corniculatum ; 
