Palmer: Effect of Pollution on River Algae 



393 



The 60 most tolerant species are given in table 4. Euglena viridis, followed 

 by Nitzschia palea, are at the top of the list with total scores of 6v^ and 46, 

 respectively. 



The names and total points for the 10 most tolerant species of a genus are 

 shown for the two leading genera, Euglena and Oscillator ia (tables 5 and 6). 

 In the former genus, the first species, E. viridis, is far ahead of the other nine 

 species. In the latter genus there is a more gradual change in total points from 



Table 5 

 Species of Euglena: Ten Most Tolerant of Pollution 



Table 6 

 Species of Oscillatorla: Ten Most Tolerant of Pollution 



one species to the next. Eight of the 10 species of Euglena and 9 of Oscillatoria 

 are among the 60 most tolerant forms as noted in table 4. 



It would be interesting to know what species of Chlamydomonas was con- 

 sidered most tolerant of organic pollution, but unfortunately very few of the 

 110 investigators have determined and recorded the species for this genus. For 

 the genus Xavicula, numerous species have been recorded by the investigators, 

 but there is little indication that there may be one or two species which are 

 much more tolerant than others that they have named. 



Additional records by other workers would undoubtedly change the com- 

 parative total points and the relative positions of the algae in both the genus and 

 species lists. This is particularly so for the algae near the low ends of the lists 

 where a relatively few reports are responsible for their present positions. 



