295 



1895 in the last five months are somewhat alike, and their 

 plankton production is somewhat similar (cf. PI. VIII. and X.). 

 In 1897, however, the uninterrupted and prolonged low water 

 yields a much larger production of plankton (3.56 for the last 

 seven months). 



Though incomplete, the evidence in a general way indi- 

 cates that 1894, in the period included in the collections, was 

 a year of abundant plankton production, approximating 2.5 



cm.^ per m.^ of water. 



1895. 



(Table III.; PI. IX., XLIII., LI.) 



Of the 50 collections of this year but 4 were made in the first 

 six months. This was particularly unfortunate, for the spring 

 was one of exceptionally low water, and the collections are so in- 

 frequent as to give only the faintest clue to the curve of plank- 

 ton x^roduction in this important period. All of the collections 

 were made by the oblique-haul or repeated vertical-haul method. 

 Omitting the very unusual catch of June 19, the mean volumes 

 of plankton, silt, and total catch per cubic meter are respective- 

 ly 2.12, 1.88, and 4.01 cm.^ As an average, the proportion of silt 

 in the catches is thus quite low — a fact explained by the absence 

 of considerable floods during the period of most frequent col- 

 lections. 



As is shown on pages 164 and 165, this was a year of unusu- 

 ally low water, the mean annual stage of the river being 3.61 ft. 

 The spring rise did not bring the river to much more than min- 

 imum bank height, and there was no June rise. Aside from a 

 few minor meteoric rises to less than 6 ft. in July and Septem- 

 ber the low-water period was unbroken until the December 

 flood culminating at 12.6 ft. at the close of the year A glance 

 at Plate IX. will indicate that the collections suffice to trace 

 the production during the last six months, — a low-water period 

 with minor rises, — and to follow somewhat closely the effect of 

 these hydrographic changes upon the volume of the plankton. 



The isolated collection of Feb. 23, made beneath 37 cm. of 

 ice at the close of a period (PL IX.) of ice blockade of approx- 



