FEEDING WITH LOW MOLECULAR WEIGHT COMPOUNDS 261 



of starch, including glycol, glycerol, methanol, phenol, acetate, lactate, 

 and butyrate. 



Treboux (1905) found that many algae, Chlorella, Stichococcus, and 

 Chlamydomonas, for instance, can live in darkness on acetate (some 

 thrive on this food even better than on glucose), and a few can use also 

 lactate, butyrate, or citrate; but they all refuse to accept other organic 

 acids, including formic, propionic, valeric, oxalic, mahc, succinic and 

 tartaric. 



Sabalitschka and Weidling (1926^) found that Elodea canadensis also can form 

 starch from acetaldehyde, both in darkness and in light, the optimal concentration being 

 0.032%, that is, somewhat higher than that of formaldehyde. (Acetaldehyde begins to 

 retard the enzymatic activity of the plant — e. g., respiration and catalase activity — 

 only at concentrations above 0.3%.) Photosjmthesis is stimulated by acetaldehyde 

 concentrations up to 0.13% and retarded above this limit. Bodndr, R6th, and Bernauer 

 (1927) and Bodndr (1928) opposed Sabalitschka's conclusions and insisted that form- 

 aldehyde alone is assimilated and thus can cause an increase in dry weight, while acet- 

 aldehyde merely reduces respiration, and thus makes the weight of the treated leaves 

 higher than that of the starved control leaves (which lose more weight by respiration). 

 It does not appear however, that this suggestion can account for all of Sabalitschka's 

 results. 



Whatever the truth about acetaldehyde is, there is little doubt that 

 acetic acid, glycol, glycerol, and many other compounds can be used 

 as foods to support plants in absence of photosynthesis. The prefer- 

 ence of many organisms for acetates has been confirmed by Lwoff (Lvov) 

 and coworkers. Lwoff (1932) and Lwoff and Dusi (1935) investigated 

 the food requirements of green flagellates (Chlamydomonas, Euglena, 

 Chlorogonium, etc.) — Protozoa of a predominantly "vegetative" char- 

 acter — which can develop in darkness provided they are supplied with 

 an organic source of nitrogen and a simple source of carbon. Lwoff and 

 Dusi found that some species thrive on propionate, butyrate, valerate, 

 caproate, pyruvate or lactate, but that the only two organic compounds 

 which all of them will accept are acetate and soluble starch (while even 

 glucose, fructose, or sucrose are rejected by some of them). Lwoff and 

 Dusi suggested that acetic acid may be the first product of carbohydrate 

 synthesis not only in Protozoa but also in the higher algae and land plants. 



In reviewing the list of simple compounds capable of supporting the 

 growth of plants in the dark, we find that they almost invariably belong 

 to reduction levels above, or equal to, that of the carbohydrates. 



Treboux was surprised that acetic acid should be preferred to the 

 common plant acids (e. g., mahc and oxalic); but consideration of the 

 reduction levels gives a plausible explanation. Compounds which can 

 be used for conversion into starch in the dark are those whose L values 

 are > 1, for instance: for glycol, L = 1.25; butyric acid, L = 1.25; 

 glycerol, L = 1.16; acetic acid, L = 1; lactic acid, L = 1; etc. Com- 



