480 FOOD REQUIREMENTS 



and Pace (1935) found that Chilomonas Paramecium survived for only 

 a few transfers in media without S. For example, one S-free line died on 

 the seventh day and others on the third, while several lines in media 

 containing S were maintained for from twenty to twenty-four days. An- 

 other example is that of Hyalogonimn klehsii, which requires relatively 

 large amounts of calcium (Pringsheim, 1937b). 



It is possible, of course, that the action of certain elements may not 

 be specific; in other words, comparable effects on metabolism may be 

 exerted by several different elements, one of which may be substituted 

 for another. This possibility should be considered in investigations on 

 food requirements of photoautotrophs and heteroautotrophs. 



Photomesotrophic Nutrition 



Euglena deses (Dusi, 1933b) may be considered an obligate photo- 

 mesotroph, a flagellate which has lost the primitive photoautotrophic 

 ability characteristic of various other green flagellates. In addition to 

 this species, several facultative photoautotrophs among the Euglenidae 

 are known to carry on photomesotrophic nutrition: E. anabaena (Dusi, 

 1933b; Hall, 1938b), E. gradlis (Dusi, 1933a), E. klehsii, and £. 

 stellata (Dusi, 1933b). An interesting feature of these Euglenidae is 

 that a particular amino acid may support growth of one species but not 

 another (Dusi, 1931). For example, phenylalanine was satisfactory for 

 E. anabaena, E. gracilis, and E. stellata, but not for E. deses and E. 

 klebsii, while serine was adequate for growth of all except E. anabaena. 

 Comparable differences were noted for several other amino acids. 



Among the Phytomonadia, photomesotrophic nutrition has been dem- 

 onstrated in Chlamydomonas agloejormis and Haematococcus plu- 

 vialis (A. Lwoff, 1932), and also in Lobomonas piriformis (Osterud, 

 1939). In addition, Loefer (1935b) observed, in Chlorogonium elonga- 

 tum and E. euchlorum, acceleration of growth by glycocoU and several 

 other amino acids, added separately and in mixtures, to an inorganic 

 medium and to a salt solution containing sodium acetate. 



The growth of photomesotrophic species may be accelerated by the 

 addition of various carbon sources (e.g., sodium acetate) to an amino- 

 acid medium. Concerning mineral requirements in photomestrophic 

 nutrition, nothing is known beyond the fact that amino acids have often 



