Experiments were performed in 1963 and in 1964 on four varieties of Vitis vinifera to determine the responses to the kinins, BTP (6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine) and BA (benzyladenine). Both kinins were effective in increasing fruit numbers, and in some instances fruit growth. BTP was more effective than BA. BTP applied to Black Corinth clusters at bloom produced berries three to four times larger than the controls, and the pedicels were much thickened. Black Corinth was treated at bloom with BTP, gibberellin, and/or an auxin, 4-CPA. Gibberellin alone and a mixture of all three compounds produced the largest berries. Berries were elongated as a result of the gibberellin. 4-CPA and BTP produced about equally sized, almost round berries. Treatment of the apical half of Black Corinth clusters at bloom with BTP at 1,000 ppm enlarged only the treated berries. Treatment of the basal portion resulted in some movement towards the apical portion.

When Thompson Seedless clusters were treated with BTP and the mixture of BTP and gibberellin, the number of berries was increased. Berry size was increased only by gibberellin or the mixture of the two compounds. At the shatter stage BTP at 1,000 ppm increased berry size although not nearly so much as gibberellin alone or the gibberellin-BTP mixture. BTP or BA applied to Thompson Seedless at shatter stage increased numbers of berries.

BTP in range from 125 to 1,000 ppm increased berry numbers in Muscat of Alexandria, as did dipping of clusters on partially defoliated shoots. The set of berries on emasculated flowers of Black Corinth, Thompson Seedless, and Tokay was increased by BTP.

Clusters of Black Corinth, Thompson Seedless, Tokay, and Almeria were dipped in BTP at 1,000 ppm at bloom stage. Far more ovaries or berries fell from the treated than from the control clusters at shatter, except for Tokay. There was a tremendous increase in the number of seedless berries on the treated clusters of Almeria.