484 



1. Other things being equal, bodies of fresh water free 

 from vegetation (submerged macro-flora) produce more plank- 

 ton than those rich in such vegetation.* Thus, the amount of 

 plankton produced (as indicated by the averages of all of our 

 collections in the several localities examined) in our open 

 waters is from two to eleven times as great as it is in our lakes 

 closed by vegetation. As shown in the table on page 429, the 

 average planktons in Thompson's and Phelps lakes are 7.94 and 

 and 19.65 cm.'^ per m.'^ respectively, while in Quiver and Dogfish 

 lakes the quantity is only 1.70 and 4.22. Flag Lake, with an 

 average of 11.46 cm.^, is an interesting exception to this con- 

 trast which will be discussed in another connection. The con- 

 trast is even more striking if the averages of the monthly 

 averages for all the years, are made the basis of comparison, as 

 in the following table and diagram. 



COMPARISON OF PLANKTON PRODUCTION IN VEGETATION-POOR AND 

 VEGETATION-RICH WATERS. 



Month 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



Gr'd av. of monthly av 



Vegetation-poor 



Quiver Lake Dogfish 



1-75 



•53 



I. ID 



I .96 

 10.50 



5-79 

 1-75 

 1.95 

 2.51 

 2.39 

 3-05 

 2.64 

 376 



3.16 



Vegetation-rich 



Thompson's pj^^jp^ Lake 



Lake 



3-79 

 1.27 

 2.96 



14.49 

 29.59 

 10.66 



4-74 

 6. 19 



5-37 

 10.64 



6.39 

 3.08 



8.26 



3-29 



5.68 



5.68 



11.77 



25-33 



11.40 



8.50 



58.12 



47-25 

 27.68 



41-57 

 21 .96 



22.35 



Ratio 



9 



4 



3 



1-5 



4 



7 



5 



20 



17 

 10 



17 

 6 



1:6 



On this basis, the waters full of aquatic vegetation pro- 

 duce throughout the whole year less plankton than waters 

 free from such growths. Relatively few exceptions to this rela- 



* This relation of vegetation to the plankton may be formulated as follows: 

 The amount of plankton produced by bodies of fresh water is, other things being 

 equal, in some inverse ratio proportional to the amount of its gross aquatic vegeta- 

 tion of the submerged sort. 



