164 PLANKTON OF WISCONSIN LAKES 



The diatom sample contained a larger percentage of ether extract 

 than any other sample of plant material. The percentage of this ex- 

 tract in the diatoms is more than two and a half times as large as the 

 maximum in the blue-green algae with the ash included, while it is 

 more than four times as large as the latter on an ash free basis. The 

 percentage of ether extract in the organic matter of the diatoms, in fact, 

 is exceeded by that in only five samples of animal material as shown in 

 part II of table 49. The large percentage of this extract in the diatoms 

 is due to the fact that the reserve material in these forms consists of 

 drops of oil instead of carbohydrate compounds. 



The percentages of crude fiber and of pentosans are relatively small 

 in this sample of diatoms, and the nitrogen free extract, on an ash free 

 basis, is substantially the same as the mean for the nine samples of blue- 

 green algae. 



Whipple and Jackson 6 found 2.2 per cent of nitrogen in the diatom 

 Asterionella, while the ash constituted 57.52 per cent of the dry ma- 

 terial. The percentage of nitrogen in Asterionella is smaller than in 

 the diatom material from Lake Mendota, while the ash is much larger ; 

 on an ash free basis the percentage of nitrogen in the former is 5.18 

 per cent as against 6.05 in the latter. (See table 51.) The ash of the 

 sample containing Asterionella contained 49.48 per cent of silica, leav- 

 ing only 8.04 per cent for the other constituents; deducting the silica 

 from the ash of the diatoms secured in Lake Mendota leaves 8.72 per 

 cent. 



For marine diatoms Brandt 7 gives the following results on an ash 

 free basis : crude protein 28.7 per cent, fat 9.0 per cent, and carbohy- 

 drate 63.2 per cent. (See table 51.) He regards the crude protein 

 in his material as rather high, but it is more than 10.0 per cent below 

 that found in the material from Lake Mendota ; the percentage of fat 

 in the marine material is only a little more than one-third as large as 

 the ether extract in this sample of freshwater diatoms. In the marine 

 diatoms the crude protein and the fat constitute only 36.7 per cent of 

 the dry organic matter, while in the freshwater forms from Lake Men- 

 dota these two items make up 60.29 per cent of the organic matter. 



On an ash free basis the nitrogen found in Asterionella by Whipple 

 and Jackson is equivalent to 32.4 per cent of crude protein as compared 

 with 28.7 per cent in the marine diatoms indicated by Brandt. 



Phanerogams. Two samples of Potamogeton were analyzed; one 

 contained mature plants whose leaves were dead and the other consisted 

 of plants whose leaves were still bright green. The stems as well as the 

 leaves of the plants were used for both samples, but not the roots. The 



6 Jour. N. E. Waterworks Assoc, Vol. 14, 1899, pp. 1-25. 

 7 Wissensch. Meeresuntersuch., Abt. Kiel, N. F., Bd. 3, 1898, p. 89. 



