In total 73 species of Euglena were ordered according to their saprobic index (S) and saprobic valency starting with species tolerating a heavy organic pollution and ending with those from most clean water . This paper is meant as an addition to the Ergebnisse der Limnologie, Heft 7 (Sladedek, 1973) .
Euglena was already used as indicator of saprobic conditions since the beginnings of the saprobity system (Kolkwitz & Marsson, 1902) . There are about 200-300 species and varieties belonging to the genus Euglena Ehrenberg . Whereas the recognition of the genus is relatively easy, the determination into species is sometimes rather difficult .
Euglena is a common inhabitant of various freshwater bodies, clean, less or more polluted and in the majority of cases eutrophicated . Generally, the representatives of Euglena show a broad ecological valency (Perman, 1956) . The same is true as concerns the saprobic conditions and individual species occur nearly in the whole extent of limnosaprobity . Huber-Pestalozzi (1955) included into his monograph a table (according to Gunther, 1927) classifying 35 species of Euglena . Palmer (1963) presented a sequence of 1o common species most tolerant to organic pollution : E. viridis, gracilis, oxyuris, acus, deses, polymorpha, intermedia, pisciformis, proxima, spirogyra . After Zelinka, Marvan and Kubidek (1959) started the application of the saprobic valency expressed in 1 o points, Sladedek (1973) classified 20 species and Cyrus & Sladedek (1973) 23 ones in this way .