337 



significant that the nitrates fall during this period of increased 

 production (Table X.) to half the content in November. The 

 average production in this month (.99) is in excess of that in all 

 previous years excepting 1895, when stable conditions of longer 

 prior duration were prevalent. The relation of stability in en- 

 vironmental conditions to increase in plankton production is 

 thus confirmed by the data of this month. 



As a whole, 1898 was a year of relatively light plankton 

 production, averaging 2.13 cm. 3 per m. 8 (mean of all collections), 

 or 2.03 (mean of monthly averages). This is all the more 

 apparent when we note (PL XII.) that production falls below 2 

 cm. 3 in all but eight weeks of the year and below 1 in all but 

 fourteen. The only large production is found in April-June, 

 and the unusual extent of this brings up the yearly average. 

 The well-defined vernal pulse under peculiarly favorable hydro- 

 graphic conditions, and the suppression of production by the 

 flushing effect of repeated floods are the prominent features of 

 the year's record. The effect of stability of environmental 

 factors in increasing production, and of instability in suppress- 

 ing it is apparent. The cyclic movement of production is also 

 to be traced throughout the year. 



1899. 

 (Tables III., X. ; PI. XIII., XLV., L1I.) 



Collections at weekly intervals were made in this year 

 through the month of March. The 13 collections afford an op- 

 portunity of tracing the effect of the interrupted ice blockade 

 which continued during the first two months in semi-flood con- 

 ditions, and of noting the effect of the early maximum spring 

 rise upon production. 



The January pulse has a duration of 21 days, — from the 10th 

 to the 31st, — with a maximum amplitude of .5 cm. 3 per m. 3 on 

 the 17th. Its mean falls on the 18th, 27 days after that of the 

 preceding pulse. This is a month of gradual though consider- 

 able change in levels, the total movement being 3.5 ft. The 

 gradual character of the rise permits the development of a 



