385 
season’s growth without a flood exceeding 7 ft. Even the rise 
to 5.2 ft. Dee. 19 was only beginning to affect the conditions 
within the lake. In October the succulent vegetation, such as 
Nymphea, Nelumbo, and Sagittaria, was undergoing rapid decay, 
which was checked by falling temperatures, and we find plank- 
ton production declining (from 57.76 to 6.38), and the decline 
accelerated on Dee. 28 (3.26) with the invasion of flood waters. 
This large production, unsurpassed at any other station (cf. Pl. 
XXXII. with Pl. [X., XXVI., XXX., and XXXVI), is to be cor- 
related with the excess of decaying vegetation in this locality 
resulting both from the abundance and character of the vegeta- 
tion and its freedom from flushing by current due to access of 
tributary waters. The maximum in October is due almost 
wholly to Synura ubella, which declines in the later collections 
in which the Cladocera and later the Copepoda appear in in- 
creasing numbers. Throughout this period there was no run- 
off until flood levels were reached late in December, and even 
then, owing to reasons above cited, the run-off from the area is 
relatively slight. There was consequently no direct enrichment 
of the channel waters from this area. Unfortunately, no chem- 
ical analyses of water from this area are available, and the 
chemical basis for an estimate of the relative fertility of this 
marsh is lacking. The data of production illustrate the great 
_ fertility of waters impounded where decaying organic matter 
abounds. Both the impounding factor and the local enrich- 
ment factor are apparently at a maximum potency here at this 
season, and production is correspondingly great. 
1896. 
(Table VII.,-Pl. XXXI1I1.) 
There are 27 collections in this year, with an average of 
13.83 em.’ per m.*, and a maximum of 203.52 on May 2. The 
weekly interval of collection in April-June enables us to follow 
the course of production withsome detail, but the fortnightly, 
or longer, interval prevalent during the most of the remainder 
