307 



The amount of oxygen present in the water in the dark, or on 

 dark nights, is reported as 0.20, 0.25, and 0.27 cm. 3 per 100 cm. 3 of 

 water. In bright sunlight in the laboratory, and with the unusual 

 abundance of Euglena due to the collection of the water sample 

 from the region of the water-bloom, it rises to 2.05 cm. 3 In the 

 case of the Spandauer samples it rises from 0.25 in the dark to 1.15 

 (an increase of 0.90 cm. 3 ) after "long" exposure to bright sunlight 

 in the laboratory. The oxygen in this water at 11 :00 p. m., after 

 exposure to moonlight, amounted to 0.45, or 0.20 cm. 3 more than 

 was found in control water kept in the dark. In this instance the 

 apparent increase due to moonlight is 2 / 9 of that due to sunlight. In 

 the case of the moonlight the analysis was made at 11:00 p. m., 

 after not more than three hours ' exposure. The moon was not at its 

 greatest efficiency, since full moon occurred four days prior to the 

 date of analysis. In the case of the sample exposed to the sunlight 

 the analysis was made at 4:00 p. m., after "langer intens Sonnen- 

 schein." It would seem probable that the effectiveness of moon- 

 light in comparison with sunlight in photosynthesis by the phyto- 

 plankton here indicated (2 to 9) is below the possible maximum and 

 also above that of the average, since it was obtained when the 

 moon was but four days past its maximum effectiveness. 



If we accept Knauthe 's data as sufficient to establish the effec- 

 tiveness of moonlight in increasing photosynthesis, and thus the 

 growth of the phytoplankton, we find in it a recurrent factor of the 

 environment to whose influence we may seek to attribute the rhythm 

 of growth of the chlorophyll-bearing organisms. 



On Plates I. and II. I have plotted the seasonal distribution of 

 the totals of the Chlorophycece, of the Bacillariacecz, and of the 

 Mastigophora from July, 1897, to April, 1899, and have indicated 

 the times of full moon throughout this period by marks at the bot- 

 tom of the diagram. The diagram shows clearly the occurrence of 

 these recurrent pulses, their approximation in the three groups of 

 chlorophyll-bearing organisms upon the same or adjacent dates, and 

 the occurrence of their maxima in some cases at the time of full 

 moon or within an interval of ten days thereafter. 



In the table which follows, I have given the data bearing on the 

 pulses of the total of all chlorophyll-bearing organisms from July, 

 1895, to October, 1896, and from July, 1897, to March, 1899, inclu- 

 sive, 36 months in all, stating the location of the pulse as determined 



(21) 



