Abstract

Observations of fruit development in the cultivated strawberry (Fragaria x Ananassa Duchesne) are interpreted as showing that, in unpollinated fruits, development of fruit tissues ceases at anthesis because of an inhibitory factor produced by the maturing carpels. It is suggested that one of the functions of pollination, or fertilization, is to remove this inhibition and make the tissues susceptible to stimulation by growth substances produced either by the parent plant or the fertilized carpels.
Receptacles in which pollination is confined to a single carpel swell only around the point of insertion of that carpel, and no swelling occurs beneath neighbouring unfertilized carpels. Likewise, after treatment of the plant with gibberellic acid swelling of fruit tissue occurred only at the base and did not extend into areas occupied by unfertilized carpels.
Parthenocarpic fruits were produced in two ways; both depended on the suppression of carpel development on the receptacle. In one case, modification of the plantsí environment resulted in the production of leafy bracts in place of carpels. In the other, carpel development was specifically inhibited by applications of maleic hydrazide at the time of carpel formation.
When carpels were only partially suppressed swelling occurred only in areas either free of carpels or occupied by fertilized carpels, never in areas occupied by unfertilized carpels.