302 PLANT GROWTH SUBSTANCES 



Extra- specific chemical regulation of sexual processes. — Among the earlier 

 works on the relationship to sexual reproduction of chemical substances, 

 nutrients, or other compounds in the medium, are those dealing with 

 the factors influencing sexuality in the water molds, members of the 

 aquatic order Saprolegniales. The works of Klebs (25,26,27), Kauffman 

 (24), Pieters (42), and Coker (15) established the general pattern of 

 environmental conditions necessary for the production of sexual organs 

 and traced the effects of many variants in the chemical environment of 

 the plant. 



The first of a large number of papers, continuing to the present time, 

 on the interspecific effects of metabolites on sexual reproduction ap- 

 peared in 1903 when MoUiard (37) demonstrated that the relative 

 abundance of ascocarps oi Ascobolus was greatly increased by the presence 

 of certain bacteria. Heald and Pool (23) described a similar stimulation 

 of the sexual process in Melanospora pampanea by the metabolic products 

 of certain species of Fusarium and Basisporium. In the latter case the 

 effective agent was shown to be a complex organic acid. Sartory (62, 

 63,64) demonstrated the effectiveness of bacteria in association with a 

 yeast and with two species of Penicillium in promoting sexual activities 

 in these fungi. Dodge (17,18) observed the beneficial effects of certain 

 bacterial associates on the fruiting of Ascobolus magnificus and also 

 pointed out the probable role of the plant's own metabolic activities 

 on the sexual process. The formation of perithecia of Thielava hrasicola 

 was likewise found by McCormick (36) to be greatly increased by 

 extracts of other fungi. The number and size of perithecia of Venturia 

 inequalis were shown by Wilson (71) to be greatly increased by a heat- 

 labile component of the filtration-sterihzed brei of Penicillium sp. 



Robinson (59), in an extensive investigation of growth and sexuality 

 in Pyronema confiuens, demonstrated the close dependence of sexual 

 reproduction on the chemical nature of the medium and the essential 

 role of light in initiating the immediate conditions for the formation of 

 sexual organs and for the development of ascocarps. Comparable work 

 on a number of species oi Phytophthora by Gadd (20), Lester-Smith (35), 

 Ashby (4,5,6,7), and Leonian (31,32,33), complicated by uncertainties 

 as to the pattern of sexuality obtaining in the genus, finally resulted in 

 the demonstration of beneficial effects upon the production of oogonia 

 and oospores by extract of peas and by extracts of numerous unicellular 

 green algae. The influence of C/N ratio upon sexual vigor in Mucor 



