385 



season's growth without a flood exceeding 7 ft. Even the rise 

 to 5.2 ft. Dec. 19 was only beginning to affect the conditions 

 within the lake. In October the succulent vegetation, such as 

 Nifrnphcea, Neluinho, and Sagitfan'a, 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 Dec. 28 (8.26) with the invasion of flood waters. 

 This large production, unsurpassed at any other station (cf. PI. 

 XXXIII. with PI. IX., 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 Si/Hiira uhidJa, 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., P!. XXXIII.) 



There are 27 collections in this year, with an average of 

 13.83 cm.^ 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 with some detail, but the fortnightly, 

 or longer, interval prevalent during the most of the remainder 



