ANALYSIS OF OBGANISMS 163 



The ether extract in Spirogyra and Cladophora is substantially the 

 same as the mean of the blue-green algae, but it is smaller than in 

 Ankistrodesmus and in Volvox. The percentage of pentosans is larger 

 in Spirogyra and Cladophora than in any of the other algae included in 

 this series of samples; on an ash free basis the percentages are sub- 

 stantially the same in these two filamentous algae, but they are more 

 than five times as large as the minimum in the blue-green algae and 

 more than eleven times as large as the percentage of the pentosans in 

 Volvox. Cladophora yielded a large percentage of crude fiber, this item 

 amounting to more than a quarter of the dry organic matter, but only 

 a relatively small percentage was found in the sample of Spirogyra. In 

 this respect the latter compares very favorably with about half of the 

 samples of blue-green algae, but it is much smaller than the percentages 

 in Ankistrodesmus and Volvox. The percentage of crude fiber in this 

 sample of Cladophora is almost three times as large as the maximum 

 of the other algae given in this table; in fact, it is the maximum ob- 

 tained in this series of samples. 



The sample of Cladophora yielded a large percentage of ash and sil- 

 ica; the material was obtained from rocks along the edge of the lake 

 and was carefully washed when it was collected, but the large percent- 

 ages of ash and silica seem to indicate that the sample contained some 

 sand. The percentage of ash in Spirogyra is only about one-third as 

 large as that in the Cladophora material, still it is appreciably larger 

 than the percentages of ash in the samples of blue-green algae. 



Part II of table 49 shows that nearly three-quarters of the organic 

 matter of Spirogyra consisted of nitrogen free extract, the percentage 

 being larger than in any other form given in the table. With the excep- 

 tion of one sample of Microcystis, the nitrogen free extract in the 

 sample of Cladophora is larger than in all of the samples of blue-green 

 algae listed in table 49. 



Bacillariaceae. The sample of diatoms obtained from Lake Mendota 

 contained several forms, but the most abundant one was Fragilaria, 

 with Tabellaria ranking second in importance. This material yielded a 

 large percentage of ash wHich consisted chiefly of silica derived from 

 the silicious shells of these organisms. As a result of the presence of 

 such a large amount of inorganic material, the percentages of the 

 organic constituents are relatively small when the ash is included. The 

 percentage of nitrogen in the diatoms, for example, is less than half as 

 large as that in the various samples of blue-green algae, with the excep- 

 tion of one sample of Microcystis. On an ash free basis, however, the 

 comparison is more favorable to the diatoms, but even then the per- 

 centage of nitrogen falls below the minimum of the blue-greens; it is 

 only two-thirds as large in the diatom sample as in the samples of An- 

 kistrodesmus and Volvox. 



