304 



ber, 1897 ; and in October, 1898. The effect of this autumnal 

 decline of temperature may also be traced in monthly averages 

 of production in the table on page 292. Rapid decline in tem- 

 perature is thus immediately followed by rapid decline in pro- 

 duction in the channel plankton. »Such correlation in decline 

 of temperature and plankton cannot, however, be found as a 

 general phenomenon in the bottom-land lakes (cf. PI. XXX.- 

 XLII.) and a causal nexus between the two declines must there- 

 fore be of limited operation and at the best highly conjectural. 

 The operation of other factors than that of direct temperature 

 is probable. 



The monthly mean of production for October in 1895 is .57 

 cm.^ approaching that of 1894 (.61) and 1898 (.24). In 1896 

 and 1897 it is much higher (1.11 and 5.95 respectively), an 

 earlier decline of temperature in 1896 (PI. X.) and a later one 

 in 1897 seeming to shift accordingly the attending decline in 

 plankton, so that the September (.38) and November (1.) aver- 

 ages respectively more nearly represent the October averages 

 of 1895. 



The November ijulse has a duration of 35 days, — from Oct. 

 30 to Dec. 4, — with a maximum amplitude of 4.37 cm.^ on Nov. 

 27. Its mean falls on the 22d, 36 days after that of the pre- 

 ceding pulse. This is also a month of continued stable low 

 water, with a slight rise of .75 ft., due to the checking of evap- 

 oration and to autumnal rains. The total movement is only .99 

 ft. at Havana. Temperatures during the first three weeks are 

 somewhat stable for this season of the year, exhibiting a range 

 of only 5.3°— from 48.5° to 43.2°. The last week, however, ex- 

 hibits a fall of 10.2°, to minimum winter temperatures and the 

 beginning of the ice blockade. Under these stable conditions 

 the plankton production in November rises to a level approach- 

 ing that of midsummer of the current year, its apex (4.37) fall- 

 ing 44 per cent, short of the August apex (7.63), and its aver- 

 age (3.02) 25 per cent, short of the August average (4.03). 

 Both volumetric (PI. IX.) and statistical data (PI. LI.) demon- 

 strate the rapid multiplication of the plankton in these stable 



