483 



impossible. That the reduction in light due to clouds does in 

 a measure affect production might be inferred from the August 

 -October records in 1896 and 1898. In the two years named, 

 cloudy days and production in August are 2 and 8, and 1.12 and 

 .91 cm.^ per m.'' respectively; in September they are 11 and 2, 

 and .38 and .69 ; and in October 3 and 16, and 1.11 and .24. Hy- 

 drographic conditions are not remarkably different in the two 

 years, and while their differences in this respect are doubtless 

 potent, causing differences in production, it still seems prob" 

 able that the fluctuations in light are also operative. In any 

 event in these three months the mean production runs higher 

 in the year of fewer cloudy days and lower in the year of less 

 sunshine. Similar relations will be found to exist generally 

 in the production of the backwaters for these months (see 

 table following p. 342). The statistical data of the synthetic 

 organisms to be discussed in Part II. of this j)aper still further 

 serve to demonstrate the correlation of light and plankton pro- 

 duction. The necessity of light for the process of photosynthe- 

 sis on the part of the phytoplankton places this factor at the 

 very beginning of the chain of relations whose later links are 

 the larger animals of the zooplankton which constitute the 

 greater proportion of the volume of the catch of the silk net — 

 the basis of the present discussion. 



VEGETATION AND PLANKTON PRODUCTION, 



It is evident that our investigations afford a unique oppor- 

 tunity of determining the effect of vegetation (the word being 

 here used to refer to the coarser aquatic growth as distin- 

 guished from the microscopic phytoplankton) upon the course 

 of plankton production with reference to both its volume and 

 constitution. 



The conclusions to be drawn from our observations with 

 reference to volumetric production, already suggested in the 

 detailed discussion of production, will be summarized and dis- 

 cussed here, though some of the data upon w^hich they rest lie 

 outside the scope of the present paper. 



