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1897 (.38) and 1899 (.28), and much more than that in the more 

 stable condition.s but lower levels of 1896. Our collections in 

 1896 and 1898 (cf. PI. X. and XII.) are frequent enough to af- 

 ford a basis of comparison of the two years. The very small 

 production in the former year (.07) as compared with the five- 

 fold greater product (.33) of the latter may find its explanation 

 in the earlier rise in temperature in 1898. In this year the 

 average temperature of surface water is 43.3^ ; in 1896, only 

 39.5\ In 1898, 40° is passed on the 10th; and in 1896, on the 23d. 



The two summits on March 22 (.77) and Apr. 5 (.53) are due 

 to the separation by a fortnight of the rotiferan and entomos- 

 tracan maxima. The later limit, Apr. 12, may therefore be 

 regarded as the probable end of this volumetric pulse, and it 

 might therefore be designated as the March-April pulse. It is 

 noticeable that the decline in this pulse follows, at a week's 

 interval, upon a check in the rising temperature (PI. XII.). 

 On April 22 the temperature (see Table III.) is 51'^; a week 

 and a fortnight later it is respectively 49.5° and 48.3°. It rises 

 to 52° on the week following. The plankton production de- 

 clines from .77 cm.^ on March 22 to .43,. 53, and .13 respectively 

 in the three weeks following. The fluctuations in production 

 during the month seem to show a very close interrelation be- 

 tween production and temperature at this degree of heat and 

 season of the year. 



The April-May pulse has a duration of 49 days, — from Apr. 

 12 to May 31, — with a maximum amplitude of 35.68 cm, ^ perm.-' 

 on May 3. Its mean falls on May 5, 44 (40) days after that of 

 the preceding pulse. The months of April and May are both 

 months of very high water, the level falling below 4 ft. on but 

 four days in the latter month. This stage of the river, exceed- 

 ing bank height, results in wide-spread overflow and fullest 

 communication between channel and backwaters. The total 

 movement in April and May was 6.7 and 5.9 ft. respectively. 

 The month of April, with the exception of the first day only 

 (see page 161), witnessing a rapid and unbroken decline from 

 18 to 11.4 ft., the decline continuing till May 15, when an early 



