Sexual Hormones in Achlya. VII. The Hormonal Mechanism in Homothallic Species

1. A simple membrane technique is described for the study of diffusible sexual hormones in matings on a semisolid medium. 2. Sexual reactions have been shown to occur regularly between mated homothallic species and [male] and [female] strains of heterothallic species. All possible matings between two homothallic species, Achlya americana and Thraustotheca clavata, and [male] and [female] strains of two heterothallic species, A. bisexualis and A. ambisexualis, reveal relationships ranging from no reaction to complete compatibility, and presumably hybridization, between the two mated plants. 3. Matings between the homothallic and heterothallic species listed above, in a semisolid medium in which interposed membranes physically separate the mated plants, prove that the initiation and coordination of the sexual interactions result from diffusible hormones. 4. Assuming similar and interactive sexual hormonal mechanisms in homothallic and heterothallic species, the results of membrane matings confirm exactly the expectations based on the reactions observed in water and agar matings. 5. The effects of hormone-containing filtrates from homothallic and heterothallic species have been reciprocally determined on species showing both types of sexuality. 6. Homothallic plants react to hormone A in a quantitative pattern similar to the response of heterothallic [male]'s to hormone A plus hormone A1. Antheridial hyphal production is but little affected by hormones A1 and A2. 7. Degeneration and/or redifferentiation of oogonial initials results from high concentrations of hormone A in nine of twelve homothallic species investigated. Oogonial development, however, is normal if delimitation of the oogonium had occurred prior to the addition of the hormone. 8. Complete inhibition of oogonial initial production results from the addition of hormone A1 in three homothallic species. 9. Three homothallic species, A. americana, T. clavata, and T. primoachlya, were each shown to secrete both acetone-soluble and water-soluble (acetone-insoluble) substances capable of inducing antheridial hyphal production on [male] heterothallic plants. Each fraction, however, induces the reaction in quantitative patterns which preclude the identities of these hormones with the hormones of the A-complex from heterothallic species. 10. The conclusion is reached that homothallic species possess a hormonal mechanism similar in broad pattern to that previously demonstrated in heterothallic species, but that striking differences in detail, possibly only as regards hormonal specificities, obtain between the mechanisms characteristic of the two types of sexuality. 11. Each homothallic species possesses, in addition to the sexual capabilities requisite to its own hermaphroditism, affinities for extra-mycelial reactions, the kind and degree of which depend upon the sexual affinities of the immediate mate. Limited evidence is presented which indicates that the homothallic species studied range, as regards extra-mycelial potentialities, from strong-[male] to weak-[male]. These correspond to the predominant-[male] intergrades of heterothallic species in that they also possess weak [female] as well as [male] potentialities. 12. The possible significance of interspecific and intergeneric reactions involving homothallic species in nature is briefly discussed.