As found earlier, supply of EDTA was obligatory for both flowering
and satisfactory vegetative growth in Wol]/ia microscopica. It is now shown that
the metal affecting growth and flowering is most probably iron. Omission of Fe
but not of Cu, Zn, Mn and B from the medium markedly affects vegetative growth.
There exists also a strong interaction between EDTA and Fe, one being largely
inactive in the absence of the other. When Fe-EDDHA is substituted for Fe-citrate
and EDTA in the medium, no great effect is seen in vegetative growth, but flowering
takes place even under continuous light. Studies with 5~Fe show that, in the
medium containing Fe-EDDHA, Fe uptake is stimulated several-fold; this is
apparently associated with the flowering condition.