THE YAN ҮКАМ RESERVOIR, VICTORIA, DD 
in one Sphaynum-pool, but in another adjacent pool, in which the same species 
is equally abundant, no zygospores are formed, although the individuals arc 
apparently under precisely the same conditions. On the whole, we are at 
present almost entirely in the dark concerning the physiological conditions 
which result in zygospore-formation in the Desmidiaceæ. The precise con- 
ditions are probably widely different for various species of Desmids, owing to 
the great differences in the normal habitats of these plants. 
Species of the Protococcoideæ never appear to become a dominant 
feature of the benthos, and few of them can even be regarded as common. 
Some species are represented all through the year except in September 
and October, and the greatest variety of forms occurs in December and 
January. 
Bacillariee.—Melosira granulata is common in March, but is otherwise 
scarce. Tabellaria flocculosa is very common in September, at a Ише when 
all other Alge (including Diatoms) are exceedingly scarce. This species 
maintains its abundance until January, thus having its maximum period 
during the vernal rise of temperature (10°-23°3° C.). On the other hand, 
Cocconeis Placentula (free-floating and unattached) is very common from 
March to July, after which it gradually decreases in abundance. This 
species therefore attains its maximum during the autumnal fall of temperature 
(183-1090). Vanheurckia viridula is one of the most conspicuous Diatoms 
of the Yan Yean benthos, being common! nearly all the year round. It has 
a minimum period towards the end of September, which is followed very 
rapidly Буа great maximum in October. For the complete annual periodicity 
of these Diatoms consult the chart (text-fig. 5, p. 33). 
Myxophyceæ.—As in the plankton there are very few Blue-green Alum 
in the benthos. Опе species of Anabena occurred from March to July, 
being most abundant in April and May, but in 1905 it produced no spores. 
Oscillatoria Agardhii was common in July, but did not occur in any other 
month, 
ПІ. THE ALG.E OF THE YAN YEAN DRAINAGE AREA. 
Poors IN THE Yan Yuan Carcumenr BASIN. 
Two pools were examined. The first one was a shallow grassy pool from 
which collections were made in October, 1905. The material consisted of 
Chlorophyceæ and Diatoms, and three species occurred in quantity. These 
were Rhizoclonium hieroglyphicum, Kiitz., Ulothrie subtilis, IKütz., and 
Spirogyra porticalis, (Vauch.) Cleve, the latter in the fruiting condition. 
Among these three dominant species the following were observed :— 
Chlorophycez.— Bulhochite sp. (sterile), Oedogonium pisanum, Wittr. (in 
the fruiting condition), О. victoriense, б. H. West (n the fruiting 
condition), Pleurotwnium | Ehrenbergii, (Bréb.) De Dary (several forms) 
D 2 
