304 



follows : " The method used is that of flushing with a hose, a crew 

 of men being kept constantly at work, taking them about a period 

 of three weeks to cover the entire system. The water is allowed to 

 run through a fire-hose at each point for a period of about ten 

 minutes." This system was in use during the years of our opera- 

 tions, and it offers no occasion for the periodic pulses in growth of 

 the organisms in question. Investigation of the discharges of dis- 

 tillery and cattle-yard wastes into the stream has not revealed any 

 periodic fertilization of the river waters from these sources. The 

 available data thus fail to exhibit any periodic rhythm in food 

 matters in solution and suspension in the river water with which 

 these pulses of chlorophyll-bearing organisms might be correlated. 



Frequent reference has been made in previous pages to the 

 appearance of pulses upon the decline of floods. Flood waters bring 

 into the river, as shown by the chemical analyses, large quantities of 

 silt and organic wastes in suspension and solution. They inundate 

 great tracts of fertile territory rich in vegetation, and thus add to 

 the available sources of food for the phytoplankton. Decline of the 

 flood affords time for decay and solution of some of the food matters, 

 and time also for breeding, and its run-off adds to the volume of the 

 plankton in channel waters. A comparison of the hydrographs of 

 the years in question (Part I., PL X.-XIII.) with these recurrent 

 pulses (PL I.) will show that many if not most of the pulses appear 

 on declining flood waters, and that many of the larger ones follow 

 the major floods. Closer analysis, however, shows that there are 

 sometimes two pulses of chlorophyll-bearing organisms on the 

 decline of a single flood, and that they may also occur upon rising 

 flood or even in its entire absence. Floods unquestionably affect 

 the amplitude of the pulses, and to some extent modify their location. 

 They seem inadequate, however, to explain their recurrence and 

 their tendency toward a uniform interval. Minima between pulses 

 also recur on declining floods. 



Energy as well as matter is necessary for the growth of the 

 phytoplankton, and its source is primarily the radiant energy of 

 the sun. A plot of the tri-daily air temperatures at Havana for 

 1894-1896 (Part I., p. 478, Fig. C) inclusive, exhibits many irregu- 

 larities, a few of which partake of the nature of recurrent pulses at 

 approximately monthly intervals, but they are too few and too irregu- 

 lar to be the basis of the recurrent growth of the phytoplankton. 



