242 BUIXETIN OF THE BUREAU OP FISHERIES. 



been included in this table because its net plankton contained a larger percentage of 

 vegetable material. 



These computations seem to indicate that the nannoplankton of Seneca Lake 

 contained somewhat more than 2% times as much dry organic matter as the net 

 plankton, while in Canandaigua Lake the former was more than 4 times as great as 

 the latter. These differences are of the same magnitude as those that have been 

 obtained on Lake Mendota in midsummer. On an average, also, it may be considered 

 that this material weighs at least 10 times as much in the living state, since most of 

 these organisms, when alive, are made up of 90 per cent or more of water. 



The results shown in this table represent only a single phase of the annual cycle, 

 and hence they do not give any indication of the yearly production of such material. 

 This latter question involves the actual turnover in stock each year and includes the 

 various relations of the organisms to each other and to their environment; the chief 

 phases of this question are the rate of reproduction of the various forms at different 

 seasons of the year, and the relations of the consumers and their foods. The whole 

 problem is very complex and would require an extended investigation for an adequate 

 solution. 



These quantities of dry organic matter in the total plankton of the Finger Lakes 

 are very much smaller than those that have been obtained for Lake Mendota, Wis., in 

 midsummer. In this latter lake the average amount for the month of July in 1915 

 and in 1916 was 40,630 kg./km.^ of sturface (362.4 pounds per acre) in that portion of 

 the lake having a depth of 20 m. or more; the average for August of these same years 

 was 31,560 kg. (281.5 pounds). The average for Lake Mendota in July is more than 

 three times the amount shown in this table for Seneca Lake and more than eight times 

 that for Canandaigua Lake. 



Comparisons have been made between the productivity of the land and of the 

 water, but such comparisons have been based upon the production of beef on the one 

 hand and of fish, or oysters, or other edible aquatic forms on the other hand. These 

 materials are what may be termed the "finished products," and statistics relating to 

 them give no idea of the relative amounts of food required or available for their pro- 

 duction. This is accounted for by the fact that data concerning the quantity of food 

 available, either directly or indirectly, for aquatic organisms have been for the most 

 part wholly lacking and at best only fragmentary in character. 



The quantitative results given above for the plankton, however, enable one to 

 make direct comparisons with the land on material which is not an end product. The 

 grass produced by a pasture is probably the best land crop for such a comparison, be- 

 cause it is less subject to artificial conditions resulting from cultivation than the grain 

 crops. Henry (1898, p. 180) cites an experiment in which a pasture consisting of blue 

 grass and white clover yielded 165,827 kg. of dry organic matter per square kilometer 

 (1,477 pounds per acre) between May i and October 15. This quantity is just a little 

 more than four times the average amoimt of organic matter maintained by the deeper 

 water of Lake Mendota in July. In other words, a fourfold turnover in the stock of 

 plankton maintained by Lake Mendota during this month would have yielded as much 

 organic material annually as the pasture in the above experiment. During the vernal 

 and autumnal maxima of the plankton the difference is distinctly less than fourfold. 

 The roots were not included in this yield of grass and, taking them into consideration. 



