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.* 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 
