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426 MR. W. WEST AND PROF, G. S, WEST ON THE 
maximum, which oceurs when the temperature of the water is at its highest 
(23:3? C.) *. 
Melosira granulata is equally interesting in its occurrence, sometimes 
appearing in such quantity as to give а Melosira-phase to the plankton. In 
Windermere it has a large maximum in April (1:7? C.); in Loch Lomond 
the maximum is from May to June (5°-13°3° C.). On the other hand, in the 
plankton of the Yan Yean Reservoir, Victoria, Melosira granulata attained 
its maximum abundance in the middle of the warm period with a water- 
temperature of 21° C. 
The apparent erratic increase of the two above-mentioned Diatoms in 
relation to the water-temperatures would appear to lend support to Whipple’s 
conclusion that temperature is of so little importance to Diatoms that it does 
not affect their seasonal distribution f. But in contrast to this, it is a matter 
of common observation that most Diatoms, even the Centric ones, have а 
decided preference for cool or even cold water, and that many of the 
plankton Diatoms attain their maxima with much constancy between certain 
limits of temperature. So that taking into consideration the multitude of 
observations on the occurrence of Diatoms in relation to the temperature, we 
are compelled to agree with Kofoidf that there are times when temperature 
is more important than food as a factor controlling the growth of Diatoms. 
Myxornvcrx.—Most of the Blue-green Algm are warm-period forms, 
occurring in greatest abundance in the early part of the autumnal decline in 
temperature, The only species which oceurs in sufficient quantity to become 
dominant is Calospherium Kiitzingianum $, and this constituent occurs 
principally in the slightly contaminated lakes, such as Windermere, Loch 
Lomond, Loch Katrine, and others ||. Sometimes Gomphospheria lacustris 
is fairly abundant in some of the low-lying lakes, and in one instance 
presented a considerable August maximum. 
Species of Anabena, Aphanizomenon, Oscillutoria, ete. are for the most 
part only of secondary importance in the British lakes, attaining great. 
maxima only on those sporadic occasions which are signalized by great masses 
of * water-bloom." This phenomenon, which does not occur in the deep, 
uncontaminated lakes, yet requires thorough investigation, and it would 
appear that its complete scientific explanation can only be obtained by 
simultaneous biological and chemical observations extending over a con- 
siderable period of time (probably 15-20 years). 
* С. S. West, in Journ. Linn. Soc., Bot. xxxix. 1909, p. 21. 
t G. C. Whipple, in Technol. Quart. vii. 1894, p. 214. 
| C. А. Kofoid, “The Plankton of the Illinois River,” Bull. Ш. State Labor. Urbana, 
Illinois, viii. article 1, May 1908, p. 54. 
$ Gomphospheria Nügeliana may occur in quantity in some of the slightly contaminated 
lakes, sometimes mixed with Celospherium Kiitzingianum or even entirely replacing that 
species. 
|| Such as Lough Neagh. 
