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THE AMERICAN NATURALIST [Vol. LIV 



prevailed can not be disregarded. What the condition was in 

 wild maize no one knows, and there is little basis for speculation. 

 But the plant has probably been in cultivation quite long enough 

 to have had its character shaped by agricultural practise. 



Directly in accord with this theoretical consideration are 

 Waller's researches,' which indicate that when corn is grown in 

 hills under ordinary field conditions, self-pollination occurs, on 

 the average, in only a little more than five per cent, of the seeds. 

 As Waller suggests, these figures may be modified by further 

 work on the problem. There is no evidence, however, that the 

 percentage of self-pollination will ultimately be found to be 

 Mgnitirantly larger than this. The genetic complexity of the 

 average plant selected at random from any ordinary agricultural 

 variety of maize is a standing evidence of the prevalence of cross- 

 pollination. 



2. The origin of protogyny in the androgynous inflorescences 

 of maize need not be sought outside the Maydese. This is the 

 regular condition in Tripsacum, at least in Tripsacum dactij- 

 Jokh which is the only species that I have had opportunity to 

 examine in flower, and it occasionally occurs in Euchlcma. 

 Collins 4 and Kempton" disregard or question the existence of 

 androgynous inflorescences in the latter genus, but the fact of 

 their occasional occurrence remains. The lowest inflorescences 

 of a teosinte plaid are almost always wholly pistillate, and the 

 highest wholly staminate. Perfect flowers have not been ob- 

 served, but between the pistillate and staminate units andro- 

 gynous inflorescences often occur. These are regularly proto- 

 gynous. Androgynous inflorescences terminating the main culm 

 are often produced in the greenhouse. The difference between 

 greenhouse plants and those grown in the open in Mexico or 

 southern Florida is fully- appreciated. Androgynous terminal 

 inflorescences are certainly of rare occurrence there, if they occur 

 at all ; but I am not sure but that they are of less frequent occur- 

 rence also in maize grown in tropical or sub-tropical countries. 

 Monuvism in the Maydea? is readily influenced by environment. 

 The physiological conditions conducive to androgyny in the 

 tassels of maize, and to a relative increase in the number of pis- 



s Waller, A. E., "A Method of Determining the Percentage of Self-polli- 

 nation in Maize," Jour. Amer. 8oo. Agron., 9. 85-37, 1917. 



*Loc. cit. Also Collins, G. X., "The Origin of Maize," Jour. Washington 

 Acad. Sci., 2: 520-530, 1912. 



s Kempton, J. H., "The Ancestry of Maize," Jour. Washington Acad. 

 Sci., 9: 3-11, 1919. 



