FOOD REQUIREMENTS 483 



grown in darkness as a facultative heteroautotroph, provided glucose 

 caramel is added to the medium. Osterud (1939) has reported growth 

 of Lobomonas piriformis in an ammonium-nitrate and acetate medium 

 for three transfers (twelve weeks) in darkness. Likewise, in a medium 

 similar to that of Osterud, growth of Euglena gracilis has been observed 

 (Schoenborn, 1939) through four successive transfers, covering a period 

 of eighteen weeks. These suggestive observations indicate that certain 

 chlorophyll-bearing flagellates may retain the ability to grow in inorganic 

 nitrogen media, even after suppression of photosynthesis. 



Heteromesotrophic Nutrition 



Heteromesotrophic nutrition has been demonstrated in several color- 

 less Phytomastigophora. The Cryptomonadida are represented by Chilo- 

 monas Paramecium, which has been grown in an amino-acid and acetate 

 medium by Mast and Pace (1933) and by Hall and Loefer (1936). 

 This type of nutrition has not yet been demonstrated in colorless Eugle- 

 nida, and E. gracilis has been grown in darkness for only a few transfers 

 in a medium containing asparagin and acetate (A. Lwoff and Dusi, 1929, 

 1931). Such results are modified by the addition of thiamine, as de- 

 scribed below. Several heteromesotrophs have been identified among 

 colorless Phytomonadida. Pringsheim (1921) found glycocoll an ade- 

 quate nitrogen source for Polytoma uvella, and comparable results were 

 later obtained for P. obtusum (A. Lwoff, 1929b, 1932; A. Lwoff and 

 Dusi, 1934). In addition, P. caudatum var. astigmata (A. Lwoff and 

 Provasoli, 1935), Polytomella agilis (A. Lwoff, 1935b), and P. caeca 

 (Pringsheim, 1935, 1937c; A. Lwoff and Dusi, 1937a) seem to be 

 capable of heteromesotrophic nutrition. On the other hand, the related 

 species, Hyalogonium klehsii (Pringsheim, 1937a), appears to be an 

 obligate heterometatroph. The chlorophyll-bearing phytomonad, Chloro- 

 gonium euchlorum, has been grown in darkness in an asparagin medium 

 (A. Lwoff and Dusi, 1935b) ; likewise, Lobomonas piriformis is capable 

 of growth under similar conditions in a glycocoll and acetate medium 

 (Osterud, 1939). 



Heterometatrophic Nutrition 



All of the colorless Phytomastigophora which have been investigated 

 appear to thrive in simple peptone media, although growth is always 

 accelerated by the addition of a suitable organic carbon source. In addi- 



