Growth and Development of Isolated Phycomyces Sporangiophores.

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Abstract
A new technique is described for culturing isolated Phycomyces sporangiophores with their bases immersed in water or solutions. P. blakesleeanus sporangiophores isolated in stage 1 and grown on water (23[degree] C; constant illumination) went through a period of little or no growth before initiating sporangia after 4-5 hours and completed stage 2-3 at about 13 hours. During stage 4 they attained the same average growth rate as sporangiophores attached to the mycelium, but stopped growing between 60 and 80 hours, while comparable attached sporangiophores continued growing for at least 120 hours. The total growth at 80 hours after isolation was the same in light as in darkness. Isolated sporangiophores did not significantly alter the pH of the water. Stage 1 sporangiophores measuring from 1.2 to 4 cm at isolation gave the same total growth, but those of 1-1.1 cm grew on the average 0.4-0.6 cm less than the longer individuals Sporangiophores isolated in stage 2-3 grew less than those isolated in stage 1, and those isolated in stage 4 grew less still. There was a pronounced dry weight increase in attached sporangiophores during stage 1, a slight further increase during stage 2-3, and an additional increase in weight during stage 4, but only when a length of 10 cm had been attained. Sporangiophores isolated in stage 1, grown on water for 64-67 hours, suffered a slight loss in dry weight and the final value was only about half of that of attached sporangiophores of the same length. Apical and/or lateral branching, abnormal for Phycomyces, occurred in 1/6 of the sporangiophores isolated in stage 1. The lateral branches usually arose just below a region of visible internal damage. The growth of unbranched specimens with the same type of injury was abnormally low. Branching and reduction in growth were induced experimentally by lack of liquid water or immersion of the growth zone, but excessive pressure applied near the base only increased the frequency of internal damage with the attendant reduction in growth, but had no clear-cut effect on the branching incidence. Isolated sporangiophores give positive phototropic curvatures in white light, and strong negative curvatures when exposed to unilateral ultraviolet illumination (280 m[mu]).