The   metabolic   pathway   for
   synthesis  of the amino acid arginine in Neurospora was established by
   providing mixes of supplements to seven different auxotrophic arginine
   mutants.
<LI> Mutants arg 47 grew if supplied with either citrulline, ornithine,
or arginine.
<LI> Mutants  arg  2  and  arg  3  grew  if supplied with citrulline or
arginine.
<LI> Mutant  arg  1  grew  only  if  arginine  were  supplied;  neither
citrulline nor ornithine enabled growth.