Inactivation of the light effect on photoblastic seeds of LACTUCA VIROSA, following treatment with authentic Anti-Gibberellins. — Some compounds chemically related to Gibberellins (derivatives and/or precursors) have been found to possess inhibitory properties on seed germination. A hypothesis has been worked out on the possibility that some morphogenetic manifestations and their change, in a test, from an inhibiting status to an active one, (and viceversa), are due to biochemical changes from Antigibberellins to Gibberellins and viceversa. We did not yet identify Antigibberellins in the flowering plants; it is difficult up to date, to know whether certain precursors and/or derivatives obtained in vitro are-or-not to be considered precursors or derivatives of gibberellins in the flowering plant. The present publication deals particularly with the antiphotoblastic action on seed germination shown by Gibberic, Epigibberic and Epiallogibberic acids, following seed irradiation. Moreover a similar activity has been shown for other compounds as Attractiligenin, Cafestol-acetate, and by the lactone of Mevalonic acid. The inhibitiug effect of Epiallogibberic acid and Attractiligenin on flowering of the long-day plant Hydrophyllum virginicum and on the stem elongation of other tests, has also been mentioned. These experiments were undertaken since 1963 (Lona, 1964).