42 



PLANKTON OF WISCONSIN LAKES 



In general the curves for ether extract exhibit the four annual phases 

 that have been noted for the organic matter and the crude protein, that 

 is, spring and autumn maxima and summer and winter minima. Thus 

 the form of these curves is similar to that of the curves representing 

 the organic matter and crude protein. Attention may be called to some 

 minor differences, however; in two of the four series of observations 

 covering the open season of the lake, the curves for ether extract reach 

 their highest points for the year during the vernal maxima, while in 

 one year, namely, 1913, the highest point of the year is reached during 

 the autumn maximum. In 1915 the maximum height of the curve is 

 found at the end of the first week in December. On the other hand, the 

 curves for organic matter and crude protein reach their highest points 

 during the autumnal periods in all four years. 



Some idea of the character of the ether extract of net plankton 

 which consists chiefly or entirely of Crustacea, may be obtained from 

 table 11 (p. 189). Samples C and D were tow net catches from Lake 

 Mendota and both contained mainly crustacean material. By far the 

 greater part of the former consisted of Daphnia, Diaptomus, and Cy- 

 clops, with a smaller portion of algal material, chiefly the diatom Fragi- 

 laria ; the major portion of the latter consisted of Daphnia, only a few 

 copepods and very little plant material being present. Sample No. 403 

 was a tow net catch from Lake Monona and contained nothing but 

 Daphnia, chiefly Daphnia pulex. The extracts possessed a fishy odor, 

 especially that of No. 403; the physical and chemical constants indi- 

 cate also that they should be classed with the fish oils. Upon standing 

 for twelve hours crystals of glycerides were deposited and the extract 

 from No. 403 solidified upon exposure to the air. 



Carbohydrates 



Quantitative determinations indicated that only small amounts of 

 sugars were present in the net plankton and no systematic study of 

 them was undertaken because it was not practical to obtain sufficient 

 material in the regular catches for such determinations. The results 

 obtained by Schuette^ are summarized in the following statements. 



1. Aqueous and alcohol extracts of the crustacean samples did not 

 show the presence of reducing sugars. 



2. Material in which the algae greatly predominated possessed re- 

 ducing sugars that were soluble in 50.0 per cent alcohol. 



3. A sample of blue-green algae and one consisting of a mixture of 

 diatoms and Crustacea contained carbohydrates that were soluble in hot 

 water. No pentoses were present but the extracts showed a slight re- 

 ducing action toward Fehling's solution. 



•Trans. Wis. Acad. Sci., Arts, and Let., Vol. XIX, 1918, p. 605. 



