400 Morphogenetic Factors 



higher concentrations of growth substances than do male flowers or 

 parts. 



It has been suggested that hormones comparable to those of the animal 

 body may influence sex in higher plants. Love and Love ( 1946) found that 

 in Melandrium dioicum sex expression is influenced by various animal 

 sex hormones applied in lanolin to the axils of leaves in which flower 

 buds are to develop. Crystalline estrone, estradiol, and estradiol ben- 

 zoate shifted the sex of the flowers toward femaleness, whereas testos- 

 terone and its propionate promoted maleness. In general, hormones 

 promoting maleness or femaleness in animals have the same tendency 

 in Melandrium. Some doubt has been cast on these conclusions by Kuhn 

 (1941), who studied dioecious species of Cannabis and Mercurialis. 

 There is no evidence that substances identical with animal sex hor- 

 mones are formed by plants. If sex in dioecious plants is determined by 

 specific substances, these have not been isolated nor can they be passed 

 from one plant to another of opposite sex by grafting (Yampolsky, 

 1957). 



Maleness in ferns seems to be related to specific substances. Dopp 

 (1950) made a water extract of the prothallia of the bracken fern which 

 stimulated the production of antheridia in sporelings 4 to 8 weeks 

 earlier than in untreated prothallia (Fig. 18-20). This can be carried in 

 agar media. Naf (1956) confirmed this and was further able to induce 

 antheridium formation on a variety of other related ferns even though 

 these did not normally produce them in culture. The extract from 

 prothallia of types of ferns that form antheridia under the conditions of 

 culture used was several thousand times more effective than were extracts 

 from types that do not form antheridia under these conditions. Such ex- 

 periments suggest that in the prothallia of all polypodiaceous ferns there 

 is a substance that stimulates the formation of male sex organs. 



Sex hormones have also been found in all the thallophytes except the 

 red algae and the basidiomycetes. Burgeff (1924) reported that in non- 

 aquatic types such as Mucor mucedo, the hyphae of two different sexes 

 ("plus" and "minus" races) influence each other by means of diffusible 

 substances. Kohler (1935) confirmed these results, and Plempel (1957) 

 has reported the activity of four substances in sexual interactions in this 

 species. Kohler found that in Phy corny ces Blakesleeanus two diffusible 

 substances are produced by each sex. Krafczyk ( 1931 ) showed that in 

 Pilobolus crystallinus at least three different processes are chemically 

 controlled: the characteristic swelling and branching of the hyphae, the 

 growth of hyphae toward each other, and the delimitation of the game- 

 tangia. Machlis ( 1958 ) has found in the water mold Allomyces a hor- 

 mone, sirenin, excreted during female gametogenesis that attracts the 

 male gametes to the female ones. 



