365 
There is thus a striking similarity in production in the 
river and lake in 1898, not only in the larger movements, such 
as the vernal pulse, the low level of midsummer, and the De- 
cember rise, but also in the minor details which differentiate 
movements at shorter intervals, suggesting in some cases, and 
demonstrating in others, the presence of coincident recurrent 
pulses of production with approximately similar locations but, 
it may often be, with more widely differing amplitudes. 
A part of this similarity is doubtless due to the fact that in 
1898 for fully five months of the year, when the river was at 
8 ft. or above, the lake was not, superficially at least, differen- 
tiated from the general bottom-land environment, and there- 
fore shares more extensively the course of production elsewhere 
than it does when its emerging boundaries delimit it as a sep- 
arate unit of environment. The similarity is not, however, con- 
fined to this period of aquatic continuity, but appears also in 
the season of delimitation, when local factors are relatively 
more potent. It is also true that even in the period of conti- 
nuity the environmental factors peculiar to the lake continue, 
though submerged or invaded,—as, for example, the chemical 
conditions, which even in flood periods exhibit a certain auton- 
omy in the lake, as will be seen on comparison of Plates XLV. 
and XLIX.,—to exercise some differentiating influence, which, 
in the presence of the apparent tendency towards similarity of 
movement in production, still produces modifications sufficient 
to stamp the seasonal planktograph with a characteristic facies, 
thus differentiating it from other localities. 
The average production for the year is 2.44 cm.* per m.° as 
compared with 2.13 in the river, so that as a whole in this year 
the outflow from this lake enriches the channel plankton. On 
the basis of yearly averages and drainage areas the net result 
is an increase from 2.13 to 2.14, arise of lessthan .5 per cent. A 
more detailed analysis of the data reveals the fact that in 7 of 
the 12 months, in January, April, and June—October, the river ex- 
ceeds the lake in production. As will be seen on Pl. XXIX., the 
remaining months are those of high river levels, when the im- 
