160 PLANKTON OF WISCONSIN LAKES 



plasmic content of the cell; the cell walls are fairly delicate and the 

 gelatinous covering yields but a small amount of dry matter. On an 

 ash free basis, the crude protein makes up from 54.12 per cent to 66.45 

 per cent of the dry weight of the organic matter, if the one sample with 

 a minimum of 41.60 per cent is omitted. 



The ether extract constituted a relatively small percentage of the 

 dry material in these ten samples of blue-green algae, ranging from a 

 minimum of 1.11 per cent to a maximum of 5.02 per cent. On an ash 

 free basis these percentages are somewhat higher. The green color of 

 the ether extract indicated that it contained a certain amount of 

 chlorophyl. 



The percentage of crude fiber was small, with the exception of one 

 sample of Lyngbya in which it amounted to 7.39 per cent of the dry 

 weight of the sample ; it was less than one per cent in four of the nine 

 samples on which determinations were made. 



Including the ash the nitrogen free extract ranged from a minimum 

 of 25.72 per cent of the dry weight to a maximum of 52.09 per cent ; it 

 exceeded 40.0 per cent in only one of the nine samples of blue-green 

 algae shown in table 49. No crude fiber determination was made on one 

 of the samples of these algae so that the nitrogen free extract can not 

 be indicated for this sample. Pentosan determinations were made on 

 eight of these samples and they show percentages ranging from 2.04 

 per cent to 7.80 per cent of the dry weight of the sample. 



On an ash free basis the nitrogen free extract constituted from 27.62 

 per cent to 54.82 per cent of the organic matter in the samples of blue- 

 green algae, and the pentosans varied from 2.20 per cent to 8.46 per 

 cent. The former is substantially a twofold variation and the latter 

 almost fourfold. 



The ash varied from a minimum of 4.31 per cent to a maximum of 

 7.81 per cent of the dry weight, so that it may be regarded as relatively 

 small in amount. Quantitative determinations of the silica were made 

 on nine samples ; in seven instances the quantity of this substance was 

 less than one per cent of the dry weight of the sample, while two were 

 higher, one yielding a maximum of 1.62 per cent. 



The various samples show not only that the different kinds of blue- 

 green algae differ somewhat in their chemical composition, but also 

 that the same form is subject to more or less marked variations in this 

 respect. The specimens of Microcystis, for example, show considerable 

 differences in their nitrogen content and smaller but distinct differences 

 in the percentages of ether extract, crude fiber and ash. The two sam- 

 ples of Lyngbya from Lake Monona also differ appreciably in their 

 organic constituents although the second one was collected only four 

 days later than the first one; the ash, however, is about the same in 



