452 PLANT GROWTH SUBSTANCES 



processes so that a characteristic morphologically limited growth habit 

 is assumed. Although a specific antagonism of inositol action by hexa- 

 chlorocyclohexane (gammexane) has been suggested by work with yeast 

 (41) and with a-amylase (44), attempts to demonstrate such a relation- 

 ship in Neurospora have been unsuccessful (80). Recent investigations 

 with the pea root (71) and with a variety of bacteria (27) have likewise 

 failed to indicate a specific interrelation between inositol and gammexane. 

 The morphogenetic effect of inositol in Neurospora may conceivably 

 be related in some way, at present unsuspected, with the effects of 

 paramorphogenic substances such as tergitol, desoxycholate, and 1-sor- 

 bose, which have been shown to alter drastically the morphological form 

 of growth oi Neurospora in a nonhereditary manner (80). The antibiotic 

 produced by Penicillium griseofulvwn has been shown by Brian to be 

 the "curling factor" which has an effect on the growth of a number of 

 fungi, including Neurospora (15), apparently similar to the effects of 

 the paramorphogenic substances mentioned above. Whatever the func- 

 tion of inositol in the growth and metabolism of fungi may be, it is at 

 all events extremely specific for meso-inositol as has been shown recently 

 with Neurospora by Schopfer (72). 



Considerably more is known in respect to the roles of the amino acids 

 as growth factors in fungi than is true for the vitamins. Most of this 

 information has been obtained from studies with amino-acid-requiring 

 mutants of fungi. These studies in general have substantiated the con- 

 cepts of comparative biochemistry in that the metabolism and synthesis 

 of amino acids have been found to be similar in fungi, in other micro- 

 organisms, and in higher organisms (see 79), For example, we may 

 mention the similarities in the metaboHsm and synthesis of the sulphur- 

 containing amino acids and of arginine. 



In addition these studies with biosynthetically deficient strains of fungi 

 have raised several general points in regard to the significance of amino 

 acids aside from their obvious roles as protein constituents. One of these 

 points concerns the metabolic relationships between certain amino acids 

 and certain vitamins of the B complex. The function of tryptophan as a 

 precursor of nicotinic acid, first suggested by animal experimentation, 

 has been elucidated by studies with mutant strains of Neurospora. The 

 findings illustrated in Figure i have shown that at least one important 

 route of nicotinic acid synthesis is from tryptophan through kynurenine, 

 perhaps hydroxykynurcnine, hydroxyanthranilic acid (12,56), and quino- 



