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 

 X3ulses 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 less than .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- 



