SEXUALITY IN PLANTS 253 



That sex determination is the result of the interaction of genetic 

 and non-genetic factors, and that no difficulty is experienced in 

 applying the hypothesis of differential factors to the diverse cases 

 in plants, is well brought out by Sharp (1925), Correns (1929), 

 Emerson (1924) and others. It may be worth while, however, to 

 examine several cases where sex determination is influenced by 

 external environment. 



Cannabis sativa (McPhee, Schaffner and Hirata) has a variety 

 " Togichi " in which Hirata found heterochromosomes in the 

 male. Sinoto (1930) also inclines to the view that in his prepara- 

 tions of this species, heterochromosomes maybe present. Under 

 normal summer conditions there is little appearance of inter- 

 sexual monstrosity, but under reduced illumination, inter- 

 sexualism and sometimes complete sex reversal takes place. 

 Attempts have been made (Schaffner) to indicate that physio- 

 logical-ecological factors determine sex and that sex chromo- 

 somes when present are but indicators of the sex condition. 

 McPhee and Hirata rightly point out that, as with other charac- 

 teristics, sexuality may have a genotype with various pheno- 

 typical expressions. Light, nutrition and the balance of available 

 reserve products to mineral salts are important environmental 

 factors controlling sex expression of the genetic sex determiners 

 in a number of plants [Maize (Riede), Arisama (Maekawa, 

 Schaffner), Morus (Schaffner), Humulus japonicus (Schaffner), 

 Thalictrum dasycarpum, Myrica (Gale)]. 



Prantl (1881), after careful work on cultures of prothalli of 

 Polypodium vulgar e, Aspidium Filix-Mas, Ceratopteris thalic- 

 troides and Osmunda regalis, came to the conclusion that the 

 food supply determines the growth of the prothallus (the ha- 

 ploid generation) and the separation of the sexual organs. Good 

 conditions, especially a sufficient nitrogen supply, favour develop- 

 ment of archegonia ($ organs), while poor conditions may result 

 in the formation of antheridia (cj organs) only. Miss Wuist 

 (19 10), working with Onoclea Struthiopteris, in which 99 per 

 cent, of the prothallia are dioecious, found that a change of 

 culture medium (soil to Beyerinck's solution, distilled water to 

 Knops) induced female prothalli to become monoecious. She 

 attributed the change to difference in balance between the effect 

 of mineral salts and light intensity stimulating female prothalli 

 to produce male organs. 



