FIRST HETEROTROPHS AND ANAEROBES 407 



the Euglena on organic substrates in the dark, or even in 

 the hght when the medium is very rich in organic substances. 

 The colourless cultures obtained in this way can live and 

 glow for many years because they can nourish themselves by 

 purely heterotrophic means. 



As early as the beginning of the twentieth century it was 

 shown that if algae were supplied artificially with organic 

 substances it had a very favourable effect on their growth 

 and development.^^ The direct experiments of A. Artari-^ 

 on the utilisation of organic substances by pure cultures of 

 algae showed that glucose, fructose, maltose, sucrose, pep- 

 tones, asparagine, lysine, glycerol, mannitol, inulin and 

 many salts of organic acids formed excellent nutrients for 

 many unicellular forms of green algae. When supplied with 

 these substances the algae develop equally well in the light 

 and in the dark. 



Later experiments" established beyond doubt that when 

 organic substances are introduced into cultures of green algae 

 they are assimilated directly. This may occur alongside the 

 process of assimilation of CO2, but in some cases this process 

 may be put out of action and the algae turn over to an 

 entirely saprophytic way of life. Under these conditions 

 blue-green algae such as Nostoc/^ diatoms and such green 

 algae as Spirogyra flourish luxuriantly. 



Working with soil algae (Scenedesmiis costulatus) B. M. B. 

 Roach^^ established that they could grow in the dark on 

 media to which glucose had been added as a carbon-contain- 

 ing nutrient. C. B. Skinner and C. G. Gardner^® showed 

 that, in pure cultures of green algae, casein, albumin and 

 glucose could serve as nutrients for the organisms. Nowadays 

 media composed of potatoes, meat peptones or wort are 

 successfully used for the culture of various algae. ^'^ 



It would appear that many blue-green and other algae can 

 use the organic materials found in mud under natural con- 

 ditions too. This is indicated by the very fact that they 

 develop specially luxuriantly in stagnant waters and in other 

 similar places which are rich in organic substances. 



The view that heterotrophy is the primary mode of nutri- 

 tion is also supported by the results of investigations on 

 higher green plants (i.e. organisms which have long been 



