The influence of removing the apical shoot and different leaves above and below the flower on the fruit-set of unpollinated pea ovaries (Pisum sativumL. cv. Alaska) has been studied. Unpollinated ovaries were induced to set and develop either by topping or by removing certain developing leaves of the shoot. Topping had a maximum effect when carried out before or on the day of anthesis, and up to four consecutive ovaries were induced to set in the same plant. The inhibition of fruit-set was due to the developing leaves and not to the apex. The third leaf above the first flower, which had a simultaneous development to the ovary, had the stronger inhibitory effect on parthenocarpic fruit-set. The application of different plant-growth regulators (indoleacetic acid, naphthylacetic acid, 2,4-dichlorophenoxyacetic acid, gibberellic acid, benzyladenine and abscisic acid) did not mimic the negative effect of the shoot.
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