490 



Matanzas Lake (PL II.) more than any other body of water 

 in our field of operations resembles Quiver Lake in the various 

 factors of its environment, only upon a somewhat smaller scale. 

 Like Quiver Lake it has free communication with the river at 

 all levels, is subject to the same conditions of invasion and 

 submergence, has an eastern sandy and springy shore with lit- 

 toral vegetation, a western one of alluvium, and, between, a 

 bottom changing from sand to mud. The depth and bottom 

 configuration are very similar, and there is a supply of creek 

 and spring water roughly proportionate to the size of the lake. 

 The two lakes are thus strikingly alike save only in the matter 

 of vegetation. The vegetation in Matanzas Lake is confined 

 to a narrow belt of the littoral zone along the greater part of 

 the eastern margin and to a little Ceratophyllum adjacent to it 

 and fringing the western shore in places. Less than 5 per cent, 

 of its area is thus occupied. Quiver Lake, on the other hand, 

 has at all times a more abundant flora, which even in the years 

 of its least development holds possession of not less than 30 

 per cent, of its area. Under these circumstances a comparison 

 of the production of the two lakes should throw some light 

 upon the effect of vegetation upon the development of the 

 plankton. 



No chronological series of collections has been 'made by 

 us in Matanzas Lake. A few isolated collections have indicated 

 that it is rich in plankton, and two thorough tests of the local 

 distribution of the plankton, made in 1896, afford a basis for 

 comparison with Quiver Lake at that time. Fifteen collections 

 with the plankton pump were made in various parts of Matan- 

 zas Lake on July 9, and twenty-five, similarly distributed, on 

 August 14. The averages of the plankton per m. s of water in 

 these collections and the amounts found in Dogfish and Quiver 

 lakes on the days following (July 10 and August 15) are given 

 in the accompanying table (p. 491). Averages for the months 

 of July and August in the several years are also given for Quiv- 

 er and Dogfish lakes. 



The production of plankton in Matanzas Lake on the dates 



