JOHN R. RAPER 3^9 



furnished by distance reactions (telomorphotic reactions). These reactions 

 include among others initiation of and correlation of organ development 

 before contact of the two sexual strains in matings in water and on agar, 

 matings with permeable membranes interposed between the two part- 

 ners, and the effects of filtrates (46,48,49). 



No less than six distinct hormones are now known to be involved 

 in the coordinative mechanism: four secreted by the male and two 

 by the female. The hormone mechanism as it appears on the basis of 

 information currently available is given in Table 2.* 



The entire sexual reaction is initiated by the simultaneous secretion 

 of three substances by the vegetative male and female plants: hormone 

 A by the female, hormone A', an augmenter of the activity of hormone 

 A, and an inhibitor by the male plant. This complex of hormones induces 

 and regulates the formation of antheridial hyphae on the male plant, 

 the number of male sexual organ primordia being a logarithmic function 

 of the concentration of hormone A and a linear function of the concen- 

 tration of hormone A' (48,49,50). The quantitative production of 

 antheridial hyphae depends also on a number of physical factors includ- 

 ing temperature, hydrogen-ion concentration, electrolyte concentration 

 (48), and under certain restricted conditions, light intensity (50). Hor- 

 mone A is known to be indispensable to the reaction, but whether this is 

 also true of hormone A' has not been determined since the only means of 

 determining the effect of hormone A' is the quantitative reaction of the 

 same plant which secretes it (49). 



The antheridial hyphae, beginning shortly after their initiation, secrete 

 hormone B which induces the initiation and controls the development 

 of the oogonial initials, the female sexual organ primordia, on the female 

 plant. The oogonial initials during the period of active growth and until 

 the time of their delimitation secrete at least one hormone, hormone C. 

 If only one hormone is involved at this stage it has two distinct effects: 

 the attraction, that is, the directional growth of the antheridial hyphae 

 along the concentration gradient to the source of the secretion, the 

 oogonial initial; and the deUmitation of a short segment of the tip of the 

 antheridial hypha as the male gametangium or antheridium, but only 



*Two subsequent papers by the author, Bot. Gaz., 112: 1-24 (1950) and Pioc. 

 Nat. Acad. Sci. (in press), deal respectively with a newly discovered, J-secreted 

 hormone and with the roles of sexual hormones in homothallic species. 



