THE YAN YEAN RESERVOIR, VICTORIA. 11 
their maximnm development at a temperature 5°—7° C. lower than the 
minimum temperature recorded for the water of the Yan Yean *. 
The great scarcity of Blue-green Algæ (Myxophyceæ) is one of the most 
remarkable peculiarities of the Yan Yean plankton. These Alow play a most 
important part in the summer plankton of the shallower European lakes, in 
which the water attains a temperature no higher than that attained by the 
water of the Yan Yean, and, moreover, falls considerably lower in the winter 
months. They likewise constitute a large part of the plankton of the lakes of 
tropical Africa f, in which the surface-temperature of the water maintains 
an average equal to the highest summer temperature of the Yan Yean. As 
the Yan Yean Reservoir occupies an intermediate position between the 
lowland lakes of temperate regions and the lakes of the tropies with regard 
to its climatological conditions, but lacks the blue-green plankton-algæ so 
characteristic of both, it is possible that the chemical composition of the water 
has а direct influence on the growth of the blue-green plankton-algze. In the 
light of this suggestion it is interesting to recall the fact that the Myxophyceæ 
constitute the principal vegetation of hot-springs f, in which the water may 
contain a great diversity of mineral constituents in solution. 
Few Flagellates occurred in the Yan Yean plankton. Mallomonas and 
Trachelomonas were both absent, but two forms of Dinobryon were not at all 
uncommon, 
MONTHLY STATEMENT OF PLANKTON FROM FEB. 1905 то FEB. 1906. 
Feb. Ath, 1905.—Desmids dominant, and a few scattered Crustacea 
(Copepods, Bosmina, and Naupli). Melosira granulata and  Dinobryon 
cylindricum var. divergens both common. 
Mar. Ath, 1905.—Desmid-flora exceedingly rich ; dominance due to great 
abundance of Staurastrum corniculatum and its var. spinigerum, S. assurgens 
var. victoriense, S. longiradiatum, S. leptacanthum, S. muticum var. victoriense, 
Micrasterias Натур, Cosmarium capitulum. var. australe, C. Hardyi, С. con- 
tractum, and С. contortum forma trigona. — Intermixed. with the numerous 
Desmids were a few members of the Protococcoidex, chiefly Glæocystis gigas 
and Spherocystis Schroeteri. A few scattered Crustacea occurred, with many 
Nauplii. Melosira granulata was abundant, and the Flagellate Dinobryon 
cylindricum, with its var. d/vergens, was also very common. 
* Vide C. II. Ostenfeld & C. Wesenberg-Lund in Proc. Roy. Soc. Edinb. xxv. part xii. 
(1906) p. 1109. 
t W. Schmidle, in Engl. Bot. Jahrb. xxxi. (1902); xxxiii. (1904). СХ also G. S. West, 
1. с. pp. 89 and 90 (34 species of Blue-green Algæ recorded for the plankton of the three lakes 
Nyasa, Victoria Nyanza, and Tanganyika). 
i W. Н. Weed, * Formation of Travertine and Siliceous Sinter by the Vegetation of Hot 
Springs" Report U.S. Geol Survey, 1887-88; G. S. West, “On some Alg: from Hot 
Springs," Journ. Bot., July 1902. 
