42 DR. а. S, WEST ON THE ALGA OF 
source of the rich and varied assortment of Algw constituting the phyto- 
plankton and mierophytie benthos of the Yan Yean. It is along the bogey 
inlets of Rana and Ottelia Creeks that one finds a rich Alga-flora such as 
would be able to furnish the mierophytie benthos, and also the plankton, 
with some of their characteristic species. It seems highly probable that 
many of the species of the littoral region are recruited by means of indi- 
viduals carried into the lake with the slow drainage from these two bogey 
creeks, and that in turn the plankton receives recruits of certain of these 
species from the littoral region. 
Some of the species common to both the plankton and the benthos reach 
their maximum development in the plankton (Feb.—April) some time before 
they attain their maximum abundance (May-June) in the benthos. In this 
respect, Cosmarium contractum (and its var. ellipsoideum), Staurasirum eor- 
niculatum (and its var. spinigerum), №. muticum, 5. leptacanthum, and 
Oscillatoria Agardhii are particularly noticeable. These species after practi- 
cally disappearing from the plankton, reappear in the littoral region, and 
under the new conditions attain a second maximum. Thus during the fall 
of temperature in the early autumnal period the mierophytie benthos obtains 
some of its constituents from the plankton. 
Turning now to a consideration of the phytoplankton, many of the species 
are without doubt derived from the microphytie benthos, and some of them 
thrive as well under limnetie conditions as they do among the weeds at the 
shores. The chief interest centres around the 23 species and 5 varieties 
exclusively confined to the plankton, and the few others which are so much 
more abundant in the limnetic region than elsewhere. Whence did they 
originate? Some of them have most probably been derived from the 
littoral region, and finding the conditions of plankton-existence eminently 
suitable, have thrived to an unprecedented degree. Some have т con- 
sequence become dominant features of the plankton throughout the greater 
part of the year, whereas either they cannot be detected at all in the littoral 
region, or the most diligent search fails to reveal more than very few Isolated 
individuals. — Mierasterias. Hardyi is a case in point. This Desmid is the 
rarest of casuals among the weeds of the littoral region, but it is the most 
conspieuous and dominating species of the phytoplankton throughout the 
entire year. It most likely had an origin from a littoral or even from a hog- 
species, and the great development of its outstanding lobes at once distin- 
guishes it from any of its bog or swamp relatives. This feature has most 
certainly been developed as a result of adaptation to a limnetic existence, 
as the outstanding lobes materially increase the floating capacity of the 
individual. The occurrence of Miecrasterias Hardyi in the benthos is merely 
accidental, and the only clue to the original species from which it has been 
` derived is such as is furnished by its morphological peculiarities. These 
point most decidedly to some form of Micerasterias mahabuleshwarensis as 
