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The application of Ethrel (2-chloroethane phosphonic acid), an ethylene-releasing compound, to monoecious cultivars of cucumber and squash and an andromonoecious cultivar of muskmelon, caused a shift towards femaleness in all three species. The increase in femaleness manifested itself in several symptoms: a decrease in the number of staminate (male) flowers, an increase in the number of pistillate (female) or hermaphrodite (perfect) flowers, and a change in flowering pattern, namely, formation of female flowers at lower nodes in cucumber and squash, and formation of hermaphrodite flowers on the main axis in muskmelon where normally only male flowers are formed in this cultivar.

Sex expression is also influenced by growth regulators (8, 9). High endogenous auxin levels (2) are associated with female tendency, and exogenous auxin treatments (5) enhance the femaleness of cucumber plants, whereas high endogenous gibberellin levels are associated with maleness (1). Ethephon [(2-chloroethyl) Ethylene evolution was determined by gas chromatography using a Packard gas chromatograph equipped with a flame ionization detector and 36-X ¼-inch alumina column. Ethylene was determined in a 2-ml sample removed from a 30-or 100-ml vessel in which the tissue was incubated for 2 hr at 25 C at a light intensity of 600 ft-c. The vessels containing 1 ml of water were sealed with rubber stoppers through which the sample was drawn. The instrument was calibrated with a 1 ,ud/l ethylene standard. The data presented are from different experiments for each table.RESULTS AND DISCUSSION Ethylene evolved from young seedlings was determined in explants cut from the hypocotyl region 1 cm below the cotyledons. The data in Table I show that 11-day-old explants of the monoecious and gynoecious types evolve similar quantities of ethylene. In plant apices tested 19 days after germination, more ethylene was evolved by the gynoecious type (Table II), and the quantities were especially large under short day conditions which promote femaleness.

Ethylene production, level of I-aminocyclopropane-1-carboxylic acid (ACC) and activity of the ethylene forming enzyme (EFE) were higher in apices of gynoecious cucumber (Cucumis sativus cv. Alma) as compared to monoecious cucumber (C. sativus cv. Elem). Application of indole-3-acetic acid (IAA) enhanced ethylene and ACC production in both cultivars. The stimulatory effect of IAA was more pronounced in gynoecious apices. Induction of ethylene production and accumulation of ACC resulting from treatment with IAA were effectively blocked by aminoethoxyvinylglycine (AVG). Content of endogenous IAA, measured by an enzyme immunoassay, was lower in gynoecious cucumber as compared to monoecious one. Treatment of gynoecious plants with the antiauxins a-(p-chlorophenoxy)isobutyric acid (PCIB) and /?-naphthaleneacetic acid (/LNAA) did not inhibit female sex expression.It appears that although exogenous IAA enhances ACC and ethylene production, endogenous IAA might not have a major role in the control of sex expression in cucumber of the Beit-Alfa type.

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