548 



cubic second-foot per square mile of the watershed of 27,914 

 square miles, and a plankton production equaling that of the 

 average for the several years of the monthly means as deter- 

 mined by our collections at Havana. 



TOTAL PLANKTON PRODUCTION. 



♦Approximate average, omitting 1894. 



It should be borne in mind that the records for 1894 and 

 1895 are very incomplete, and do not as accurately represent 

 the production as do those of later years. The change in dis- 

 charge from year to year has also been computed as directly pro- 

 portional to the average river stage. This is necessarily only a 

 rough approximation, for discharge generally increases and 

 decreases in greater ratios than river stages, so that the differ- 

 ences between the several years are probably greater than the 

 figures indicate. 



While the amounts given in the table are based on some 

 conjectural factors, it may still be that more significance at- 

 taches to the direction of the differences in total production in 

 the several years. The total production varies, it seems, con- 

 siderably from year to year, the greatest departures from the 

 mean being + 40 per cent, in 1897, a year of high production 

 and river levels above the average, and — 58 per cent, in 1896, 

 when recurrent floods checked production, at least at Havana, 

 in the upper river, though it is not improbable that if the back- 

 waters and the lower river were taken into account this seem- 

 ing deficiency would be largely removed. These divergences 

 from the mean total production are considerably less than 

 those from the mean plankton content, 2.71 cm.^ per m.^ which 



