Sexual Hormones in Achlya

The sexual reproductive process of Achlya ambisexualis, a heterothallic form belonging to a well known and widely distributed genus of saprophytic aquatic fungi, is initiated and coordinated by means of specific substances (Raper, 1939, a). Four of these substances have been demonstrated (Raper, 1939, b, 1940) in the r&es of initiators and coordinators of the various stages in the sexual process. The entire process is initiated by the secretion from the female plant of hormone A which brings about the formation of male sexual organ initials, thin thread-like filaments or anther&dial hyphae, on the male plant. The antheridial hyphae then secrete the second of the specific substances, hormone B, which causes the formation of female sexual organ initials, oogonial initials, on the female plant. The oogonial initials, when fully formed, secrete the third substance, hormone C, which has two specific actions on the antheridial hyphae of the male: (1) It causes a directional growth of the antheridial hyphae, so that they grow to and become applied to the oogonial initial, the locus of the production of hormone C. (2) Once the tip of an antheridial hypha becomes applied to the walls of an oogonial initial, hormone C is necessary for the differentiation of the small male sexual organ, the antheridium. Finally, after they are differentiated from the antheridial hyphae, the antheridia secrete a fourth specific substance, hormone D, which brings about the differentiation of the female sexual organ, the oogonium, from the oogonial initial. The differentiation of gametes and the process of fertilization follow to form oospores (zygotes). The discovery of this mechanism pointed to a number of possible lines of investigation. Of these possibilities, that relating to the chemical nature and identity of the several specific substances was particularly interesting to the authors of the present account. The first of the four