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WILLIAM J. ROBBINS 



volved in the growth of even the simplest organism, or to put a limit on the 

 number for which some organism may not eventually be found to exhibit a 

 deficiency. 



Some species or strains exhibit a complete deficiency for one or more 

 essential metabolites. They are unable to synthesize any of the substances in 

 question and do not grow unless the substances are supplied in the medium 

 in which they are cultivated (Robbins and Ma, 1942). Others suffer from 

 partial deficiencies, that is, they grow slowly in the absence of a particular 



Fig. 7.1 — Growth affected by complete and partial deficiencies for essential metabolites. 

 Fungi grown on mineral-dextrose medium containing asparagine and purified agar and 

 supplemented as follows: (1) no addition; (2) thiamine; (3) pyridoxine; (4) biotin; (5) thia- 

 mine and pyridoxine; (6) thiamine and biotin; (7) pyridoxine and biotin; (8) all three vita- 

 mins. .\bove, Ceratosiomella midtiannulata, complete deficiency for pyridoxine, partial for 

 thiamine; below, C. microspora, complete deficiency for thiamine, biotin, and pyridoxine. 



essential metabolite but more rapidly if it is added to the medium (Fig. 7.1). 



For example, the clone of excised tomato roots, with which we have 

 worked for many years, suffers from a complete deficiency of thiamine and a 

 partial deficiency of pyridoxine. It will not grow unless the medium contains 

 thiamine or its equivalent. When pyridoxine is added to a medium contain- 

 ing thiamine, the growth of the excised roots is markedly increased. 



In a sugar, mineral-salt solution, the growth of our clone of excised tomato 

 ri)ots is limited by its ability to synthesize thiamine. In a thiamine solution, 

 growth is limited by the ability of the roots to synthesize pyridoxine (Robbins, 

 1946). We have not been able to define what limits the growth of the root 

 in a solution which contains both thiamine and pyridoxine. Other examples 



