Growth of isolatedPhycomyces blakesleeanussporangiophores was not promoted relative to growth on water either by a synthetic medium with two concentrations of dextrose or by concentrated and dilute potato dextrose solutions. A range of sucrose and dextrose concentrations also failed to promote growth. On the contrary, the more concentrated nutrient media and the pure sugar solutions at 0.08ensp;Mand higher reduced the final sporangiophore length measured after 64ensp;h. The inhibition on dextrose was directly proportional to concentration up to about 0.7ensp;Mand increased more sharply at higher concentration, becoming complete at close to 1ensp;M. At 0.9ensp;Mthe incidence of branching was greatly increased. Sucrose caused almost the same inhibition as dextrose up to 0.3ensp;M. On complete nutrient media, but not on water, considerable regeneration of mycelium occurred at the sporangiophore base, and the amount regenerated was greater on potato than on synthetic media. Sporangiophore growth was not influenced by the regenerated mycelium. Differences between the submerged regenerated mycelium and surface mycelium are pointed out. Growth of isolated sporangiophores was not affected by pH between 3 and 7.6, but pH 2 caused limited inhibition. The evidence suggests that a factor limiting the growth of the deficient isolated sporangiophores is normally supplied by the mycelium but is not a nutrient or growth factor present in media which support growth of mycelium with sporangiophores.
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