ANALYSIS OF OBGANISMS 165 



sample consisting of green plants yielded a larger percentage of nitro- 

 gen and of ether extract than the one containing the mature plants, but 

 the reverse was true of the pentosans, the crude fiber, and the ash. 

 Small differences in the ash are not very significant, however, because 

 the leaves are covered with a deposit of lime which comes off very read- 

 ily when the plants are dry ; it is very difficult to prevent a slight loss 

 of this lime while the material is being dried and prepared for the 

 analysis. 



The percentage of nitrogen is smaller in these two samples of Potamo- 

 geton than in the other two samples of phanerogams, namely Vallisneria 

 and Myriophyllum. In Vallisneria the percentage of nitrogen is sub- 

 stantially the same as it is in the sample of Cladophora, but it is smaller 

 than that in the sample of Spirogyra. On an ash free basis the per- 

 centage of nitrogen is smaller in the sample of Vallisneria than in those 

 of Cladophora, Spirogyra, or Myriophyllum ; of these four samples the 

 last one has the largest percentage of nitrogen, but even this maximum 

 is much smaller than the percentages shown for the various samples of 

 blue-green algae, or than those of Ankistrodesmus and Volvox. 



The two samples of Potamogeton yielded a smaller amount of ether 

 extract than those of Vallisneria and Myriophyllum; the latter rank 

 with Spirogyra and Cladophora in this respect. The sample of mature 

 Potamogeton gave a smaller percentage of ether extract than the one 

 containing green plants. 



On an ash free basis the crude fiber constituted from 16.52 per cent 

 to 21.16 per cent of the dry organic matter in these four samples of 

 phanerogamic plants. The maximum here is exceeded only by the per- 

 centage found in Cladophora. The percentages of pentosans are about 

 the same in the samples of Potamogeton as in those of Spirogyra and 

 Cladophora, but they are smaller in Vallisneria and Myriophyllum. 



The percentage of ash is fairly large in the four samples of phanero- 

 gamic plants, being exceeded among the plants only by the sample of 

 diatoms and that of Cladophora. 



The nitrogen free extract is rather large in these four samples of 

 the large aquatic plants also, ranging from 51.20 per cent of the dry 

 organic matter in Myriophyllum to 65.55 per cent in the mature Pota- 

 mogeton. The maximum percentage is exceeded by only one other sam- 

 ple of plant material, namely, that of Spirogyra. These percentages of 

 nitrogen free extract are comparable to those that have been obtained 

 for such land crops as alfalfa and timothy hay. 



Animals 



Samples of the more common forms of the plankton Crustacea were 

 secured for analysis. The Copepoda are represented by Diaptomus, 



