The transition from vegetative to fertile tissue inFucus vesiculosus

At various stages of receptacle development, segments of Fucus vesiculosus thallus subtending the fertile tips have been grown in culture. At the times of gamete maturation and gamete shedding a number of both reproductive and vegetative branches are regenerated from the wound callus. This is the only region of the Fucus thallus which has been found capable of regenerating fertile receptacles. The effects of a number of growth regulatory substances were studied. 1-naphthoxyacetic acid stimulated budding but no substance increased the proportion of fertile branches. Extracts prepared from mature receptacles did not induce the regeneration of fertile branches from vegetative thallus, but they markedly inhibited the regeneration of any branches. Subsequent estimations of the growth regulatory substances in the receptacles showed that there was a marked increase in growth inhibitors during gamete development. Growth stimulatory substances were also present but these were masked in crude extracts by the amount of inhibitors.