Chemically Induced Parthenocarpy in Certain Horticultural Plants, with Special Reference to the Watermelon

No parthenocarpy, vegetative or stimulative, other than that due to hormone treatment, occurred in the watermelons and other species of Cucurbita tested, except for cucumber and pepper. 2. A very limited number of pollen grains did not cause the watermelon to set fruit. By adding a growth substance, however, mature fruits were obtained. 3. Treated watermelon flowers which did not develop and mature parthenocarpic fruits yet persisted on the vine, apparently because the substances prevented the formation of an abscission layer. 4. No apomictic seed of any sort developed in the parthenocarpic fruits produced from growth substances. 5. A mixture of two growth substances gave better results than one alone; for example, indolebutyric acid, acenaphthene, and sulfanilamide induced parthenocarpy when employed alone, but gave more favorable results when mixed with other substances. 6. Indolebutyric acid (1-5 per cent), acenaphthene (10 per cent), and sulfanilamide (1.5 per cent) in lanolin paste failed to induce parthenocarpic development in watermelon. 7. Naphthaleneacetic acid had a greater effect on parthenocarpic development than its potassium salt and other growth substances. 8. There were great variations in fruit size and seed-coat development among the parthenocarpic fruits. Normal-sized hard seed coats were occasionally present in some fruits; however, seedless fruits of normal size which lacked seed coats were present in many species or certain varieties within the same horticultural group. 9. Pre-treatment of watermelon seeds with proper dosage of colchicine prevented development of integuments into seed coats on parthenocarpic fruits. Mixing the colchicine with a growth substance in the paste applied to the cut style did not prevent such seed-coat development.