STIMULATION BY ASSOCIATIVE INTERACTION 289 



These two growth factors appear to be necessary for a large num- 

 ber of fungi, as is indicated by rather numerous reports of trials. 



Schopmeyer and Fulmer (1931) indicated that bios is produced 

 by Aspergillus niger, A. clavatus, and Trichoderma lignorum, as 

 judged by the ability to stimulate the growth of yeast. On the 

 other hand, Williams and Honn (1932) have shown distinct stim- 

 ulation in growth by the addition of yeast extract to media on 

 which Aspergillus niger, Mucor racemosus, Microsporum fulvum, 

 Monilia metalondinensis , and M. macedoniensis were grown. 

 They called these stimulatory substances "nutrilites." A recent 

 summary by Williams (1941) reviews pertinent literature on nu- 

 trilites, which have been identified as biotin, inositol, pantothenic 

 acid, pyridoxin, and thiamin. 



Leonian and Lilly (1940) have shown that certain thiamin- 

 requiring fungi are greatly influenced by specific amino acids and 

 by zinc, iron, and other minor elements. 



Extracts from different fungi and from bacteria have been used 

 experimentally to stimulate the growth of fungi, but in most cases 

 little is known of the nature and properties of the extracted sub- 

 stances. Such studies are worth while, but the value of similar 

 investigations will be greatly enhanced if, in the future, more 

 attention is devoted to analyses to determine the identities of the 

 extracted materials. Evidence is given in one study [du Vigneaud 

 et al. (1940) ] of the identity of biotin and vitamin H. 



Both growth-stimulating and growth-inhibiting factors would 

 be expected to be present in extracts from fungi. Such a situation 

 was encountered by Satoh (1931) with Ophiobolus miyabeamis. 

 When the liquid on which this fungus had been grown was passed 

 through a Chamberland (F) filter, a material stimulatory to 

 Aspergillus niger was contained in the filtrate, and one inhibitory 

 to the same fungus was retained on the filter. The stimulatory 

 component proved to be thermostable and the inhibitory one 

 thermolabile. 



Stimulation of reproductive activity. The opinion was 

 long ago voiced that some chemical attractant aids in bringing 

 together plant sex cells of opposite potentialities. De Bary (1881) 

 supposed that this was true of fungi and also that such substances 

 were operative in stimulating the production of antheridial and 

 oogonial branches among certain Phycomycetes. Ever since the 

 discovery of heterothallism the same opinion has been entertained 



