40 PLANKTON OF WISCONSIN LAKES 



Quantitative determinations of four forms of nitrogen were made by 

 Schuette 2 on five samples of plankton; the results of his analyses are 

 shown in table 9 (p. 188). With respect to the material which he used 

 for these analyses it may be said that it was collected in 1913, the first 

 four samples in October and November of that year, and the fifth in 

 December. A and B were regular pump catches so that they contained 

 the same organisms as the net plankton of this period ; that is, diatoms 

 and Crustacea were the chief constituents. The material in C and D 

 was obtained with tow nets so that only the larger organisms were se- 

 cured, hence it contained a larger proportion of plankton Crustacea. 

 Sample E consisted almost entirely of two algae, namely, Aphani- 

 zomenon and Anabaena. 



It will be noted that by far the greater portion of the total nitrogen 

 in these samples was found in the form of mono-amino nitrogen, while 

 di-amino nitrogen was next in importance. These two forms of nitrogen 

 constituted from 77.0 per cent to 85.0 per cent of the total nitrogen in 

 these samples. From 9.0 per cent to 12.0 per cent of the total was found 

 in the form of ammonia nitrogen and about half as much in the form 

 of "humic" nitrogen. The highest percentage of "humic" nitrogen 

 was found in sample E which consisted of the two blue-green algae. 



Ether Extract 



The ether extract from the net plankton contains the fats, more or 

 less chlorophyl according to the relative abundance of the algae in the 

 sample, and probably other substances, such as lecithin, which are 

 widely distributed in plant and animal material and which are soluble 

 in ether. The presence of chlorophyl is clearly indicated by the green 

 color which it imparts to the extract, but no attempt has been made to 

 ascertain the quantity of the various substances, in addition to the fat, 

 which are extracted by the ether. It is believed, however, that such 

 materials constitute only a very small part of the whole extract. 



There are marked differences in the percentage of ether extract ob- 

 tained from the different organisms as well as differences in the same 

 organism at different seasons of the year. In general the extract from 

 the algae varies from slightly more than one per cent to about 4.5 per 

 cent of the dry weight. On the other hand a much larger percentage is 

 obtained from the Crustacea, ranging from a minimum of about 4.0 per 

 cent to a maximum of approximately 40.0 per cent. The highest per- 

 centage was obtained from the copepod Limnocalanus which usually 

 contains a large globule of oil in the thoracic region of the body. An- 

 other copepod, Cyclops, yielded 20.0 per cent of fat. There is a rather 



2 Trans. Wis. Acad. Sci., Arts, and Let., Vol. XIX, 1918, p. 604. 



