FOOD REQUIREMENTS 487 



1931, 1932, 1935a, 1935b, 1938a), who proposed a class of "Oxy- 

 trophes" to include organisms showing marked acceleration with acetate. 

 Acceleration of growth by several alcohols has been reported by 

 Provasoli (1938c) in Astasia chattom, A. quartana, Polytomella caeca, 

 Polytoma ocellatum, and Chilomonas Paramecium. 



For chlorophyll-bearing flagellates maintained in darkness, the effects 

 of various carbon sources on growth seem to be much the same as for 

 the colorless species. The growth of several species of Euglena (A. Lwoff 

 and Dusi, 1929, 1931; Dusi, 1933a; 1933b; Jahn, 1935c, 1935d; Hall, 

 1937d) is accelerated by salts of certain fatty acids, particularly acetic, 

 just as in the case oi Astasia (A. Lwoif and Dusi, 1936). Jahn (1935d), 

 in comparing the effects of certain salts on growth of £. gracilis in dark- 

 ness and in light, found that butyrate and acetate were most effective in 

 either case, while lactate produced a much greater acceleration in dark- 

 ness than in light. Succinate was toxic in light, but produced a slight ac- 

 celeration in darkness. Comparable effects of fatty acids have been re- 

 ported in several Phytomonadida — Chlamydomonas agloeformis and 

 Haematococcus pluviatis (M. Lwoff and A. Lwoff, 1929), and Chlovo- 

 gonium elongatum and C. euchlorum (Loefer, 1935a). Accelerating 

 effects of carbohydrates on the growth of Euglena anabaena in darkness 

 have also been noted (Hall, 1934) . 



Elliott (1935b) has described acceleration of growth by acetate and 

 butyrate in the ciliates Colpidium campylum and C. striatum, the effects 

 being limited to the pH range 6.5 to 7.5, approximately. The increases 

 ranged from about 15 percent to 300 percent at different pH values. 

 Accelerating effects of pimelic acid on C. campylum also have been 

 reported (Hall, 1939c), but the substance was used in low concentra- 

 tions and may have been important as a catalyst, rather than as a carbon 

 source. 



Trophic Specialization 



In this brief survey of the food requirements of Protozoa, it has been 

 pointed out that different methods of nutrition may be exhibited by 

 different members of the same family or even of the same genus. Such 

 varying degrees of specialization are particularly interesting, in that they 

 afford a basis for speculation concerning the evolution of the more 

 animal-like Protozoa from the plant-like flagellates. 



Theoretically, the evolution of animal-like flagellates from chlorophyll- 



