GROWTH FACTORS 21 



fungus. Phycomyces was used by Bonner and Erickson (1938) 

 to assay thiamin. Williams and his associates at the University 

 of Texas, who have devised several ingenious methods, em- 

 ployed yeast and various bacteria. The nutritional need for vita- 

 mins by fungi has been employed in bio-assavs of the thiamin 

 content of green plants [Burkholder and McVeigh (1940)1. 

 When they grew Floy corny ces blakesleeanns in solutions contain- 

 ing minerals, glycine, and glucose with additions of crystalline 

 thiamin, they were able to substitute small quantities of plant 

 tissues for thiamin. By comparison of the weights of the mycelial 

 mats in the cultures supplied with crystalline thiamin with those 

 of the mats in the cultures in which plant tissues were substi- 

 tuted, they could calculate the thiamin content of the green- 



i & 



plant tissues. 



The work of Robbins and Kavanaugh (1938) shows that some 

 organisms are able to synthesize thiamin, which is composed of 

 pyrimidine and thiazole; others can carry out the synthesis if 

 either or both constituents are furnished them; a third group must 

 be supplied with the intact compound if they are to grow nor- 

 mally. Robbins and Kavanaugh found that Floy corny ces nitens 

 will grow in a nutrient solution containing dextrose, asparagine, 

 and mineral salts if 30 units of pyrimidine and thiazole are added, 

 but that neither of these intermediates alone is effective. Quite. a 

 different reaction was noted with Floytoplotloora fagopyri, Fytlo'mm 

 butleri, P. polycladon, Sclerotium delphinii, S. rolfsii, and Sploaeru- 

 lina trifolii. Each of these species grows well in this nutrient solu- 

 tion if 30 units of pyrimidine are added, but thiazole alone is in- 

 effective. By Allomyces kniepii and Blastocladiella variabilis, too, 

 thiazole alone is not utilizable [Quantz (1943)], but a mixture 

 of thiazole and pyrimidine is equally as good as thiamin. 



Such synthesizing capabilities are further exemplified by the 

 researches of Leonian and Lilly (1940). They report that 

 Fusarium niveum and Rloizopus minus possess the ability to syn- 

 thesize thiamin when grown on a substrate of inorganic salt, amino 

 acids, and dextrose. On the same medium Floy corny ces blake- 

 sleeanns can also form thiamin, but only when furnished with 

 pyrimidine and thiazole. Fytloiomorploa gonapodioides can elab- 

 orate its own thiazole and, if supplied with pyrimidine, will link 

 the two substances together to form thiamin. Finally, Mucor 



