FINGER LAKES OF NEW YORK. 24I 



of material per unit of surface. In general, these lakes may be regarded as poor in net 

 plankton, the usual characteristic of lakes as large and as deep as these. 



The figures given in the various tables represent the amount of material that is 

 present on a particular date — that is, the standing crop at that time — but they do not 

 indicate the quantity of such material that is produced annually. Production and 

 destruction are processes which continue throughout the year, so that it is a very difficult 

 problem to ascertain just how much net plankton is produced annually by a lake. 



NANNOPLANKTON. 



The nannoplankton includes the various forms of plants and animals which are so 

 small that they readily pass through the meshes of the bolting-cloth strainer in the plank- 

 ton net and are lost. These small organisms are easily obtained with a centrifuge. • 

 The results obtained in these enumerations on the three Finger Lakes of New York 

 and on Green Lake, Wis., are shown in Table 21. 



The Protozoa were represented by rhizopods, flagellates, and ciliates. The rhizo- 

 pods consisted of Amoeba and some other forms which were not definitely identified. 

 A minute Monas-like form was the most numerous flagellate found, while Cryptomonas 

 was present in considerable numbers in Canandaigua and Seneca Lakes. A disk-shaped 

 flagellate was noted in the upper strata of Cayuga and Green Lakes. Synura was also 

 present in the surface stratum of Canandaigua Lake. 



The only representative of the ciliates was Halteria. It appeared in the upper 

 strata of Canandaigua and Cayuga Lakes. 



The green and blue-green algEE consisted of Scenedesmus, Oocystis, and Aphanocapsa. 

 A colonial form composed of very minute cells, 25 to 100 or more, embedded in a gelat- 

 inous matrix, has been referred to the genus Aphanocapsa. It appears to be widely 

 distributed, geographically, since it has been found in all of the Wisconsin lakes from 

 which nannoplankton has been obtained, and also in the three Finger Lakes. This alga 

 has usually been fairly evenly distributed throughout the entire depth of the various 

 lakes. This phjrtoplankton and the monads constitute the most common elements, 

 numerically, of the nannoplankton. 



The water bacteria belong to this group of plankton organisms, but they were not 

 taken into consideration in these investigations. 



No attempt was made to determine the amount of nannoplankton by weight, but 

 some results that have been obtained on Lake Mendota, Wis., will serve as a basis for 

 making a rough estimate for the Finger Lakes. The studies on Lake Mendota covered 

 a period of more than two years and they consisted of both gravimetric and numerical 

 determinations. The dry organic matter of the nannoplankton varied from a mini- 

 mum of approximately 0.8 gr. to a maximum of 3.1 gr. per cubic meter of water. The 

 numerical determinations which correspond most closely to those of the Finger Lakes 

 average about i .0 gr. of dry organic matter per cubic meter of water, so that this figure 

 may be taken as a basis for estimating the amount of nannoplankton material in the 

 latter. The results of this estimation are shown in Table 22, and also the results for 

 total plankton. In the latter it has been assumed that the crustacea and rotifers 

 furnished 75 per cent of the organic matter of the net plankton. Green Lake has not 



