COLUNS: INTOLERANCE TO SELF-FERTIUZATION 311 



would be eliminated. It now appears, however, that the growing 

 of a variety in a new environment may result in accentuating 

 the proterandrous character. Since the investigations with 

 primitive types have been conducted in this country with in- 

 troduced material, it may be that the observed proterandrous 

 tendency of these types is due largely to environmental causes. 

 The idea that maize may be of hybrid origin makes possible 

 another explanation of why maize is synacmic and at the same 

 time intolerant of self-pollination. 



Euchlaena, the nearest relative of maize and usually regarded 

 as an ancestor, is not intolerant of self-fertilization. Com- 

 parisons of selfed and crossed strains of Euchlaena do not show 

 a measurable reduction of vigor as a result of self-pollination, 

 and there is no difhculty in maintaining vigorous selfed strains. 

 In fact, as a result of the excessive branching that obtains in 

 Euchlaena, a very large proportion of the seed is normally self- 

 pollinated. Intolerance of self-fertilization is therefore among 

 the characters of maize that must be sought outside Euchlaena. 



If intolerance of self-pollination were derived from some other 

 source than Euchlaena, it seems not unreasonable to suppose 

 that the ancestor possessing this intolerance would have also 

 some means of securing cross-fertilization, which is not necessary 

 in Euchlaena. This means is suggested by another non-Euch- 

 laena character, the tendency to produce perfect flowers or 

 androgynous inflorescences which are proterogynous. 



Whenever both stamens and pistils are developed in the same 

 maize inflorescence, the silks appear before the pollen falls. 

 This is true for both terminal and lateral inflorescences. Termi- 

 nal inflorescences mature before the lateral, and since the normal 

 pistillate inflorescence has the lateral position, the delay at- 

 tendant on this position neutralizes the natural proterogyny, 

 with the result that maize plants generally are synacmic or 

 proterandrous. There is thus a sense in which maize is pro- 

 terogynous, the proterandry being that of the plant instead of 

 the individual flower or inflorescence and resulting from the 

 separation of the sexes into difi"erent parts of the plant. 



