THE YAN YEAN RESERVOIR, VICTORIA. 9 
comparative coolness of the water relative to the maximum air-temperature 
is most probably due to the supply conveyed along the aqueduct from the dams 
fed by streams which drain the mountain slopes to the north. The constant 
influx of this cool water may also account for the slowness of the changes т 
temperature of the water following on considerable variations in the atmo- 
spherie temperature. 
There 13 an average daily evaporation from the Yan Yean Reservoir of 
1,197,000 gallons, or d inch of the depth. 
A chemical analysis of the Yan Yean water-supply furnished to Mr. Hardy 
by the Metropolitan Board of Works of Melbourne shows a somewhat 
unusual proportion of chlorides, but otherwise the data are in no way 
remarkable. 
Chemical. Analysis of Melbourne Water Supply. 
[For year 1905 only. | 
In parts per 1,000,000. 
| _ 
| | | 
| "M i Date, Total solid Free Albuminoid | Oxygen us 
| Where taken. 1905. | matter. | Ammonia. Ammonia. | consumed. Ohlorine. 
— "EMEN "omn | em | ou | uas 
| Silver Creek ............... Nov. 1 53 0010 | 0:064 280 14:0 
| Wallaby Creek — ......... Mayl. 58 0:018 0:152 1535 | 150 
| | 
| | Мау 1 78 0:058 0:212 9:55 175 
| Toorourong Reservoir | | | 
| | Nov. 1 | 74 | 0028 0:134 | 530 | 190 | 
| Yan Yean Inlet ......... May 1 | 70 0:058 (0166 | 905 | 180 | 
| | 
| May1 6 0-027 0119 | 325 | 910 | 
Yan Yean Outlet ...... | | | 
|| Nov. 1 | 68 0:010 0:138 | 345 | 200 
The Yan Yean Reservoir has a very rich phytoplankton, which reaches its 
greatest development in March and April, at the time when the Crustacea are 
least evident. The collections were made over precisely the same course on 
each occasion, and only from the open water away from the shore. I have 
regarded the material as true plankton as contrasted with the benthos which 
occurs at the weedy shores. The minimum amount of phytoplankton occurs 
in September and October, in which months it is almost wanting. 
The most striking feature of the plankton is the richness of its Desmid-flora, 
in this respect offering a close comparison with the plankton of many of the 
lakes of the western British areas. This Desmid-flora is of exceptional 
interest because of the Australian types abundantly contained in it. The 
Desmids are dominant from about the middle of February to the end of 
April, reaching their greatest maximum in March and April, The most 
