No. 631] SHORTER ARTICLES AND DISCUSSION 



L86 



of hybrid origin takes care of this difficulty by attributing this 

 genetic peculiarity to the unknown parent, which hybridized 

 with teosinte, and in which cross-pollination was probably 

 secured by protogyny. 



Three fallacies render this argument inapplicable to the prob- 

 lem that it attempts to solve : 



1. We are at once confronted with a question as to how maize, 

 embarrassed by its well-known intolerance of inbreeding and by 

 the extensive self-pollination with which Collins characterizes it, 

 has persisted through the ages. The answer is that self-pollina- 

 tion in the plant is not so common as would be inferred from 

 Collins' discussion. 



It is true that a single isolated plant is largely self-pollenized, 

 if pollenized at all, but data derived from the single-stalk culture 

 often practised in experimental work can not be accepted as a 

 criterion, for maize is normally grown in hills, and prnbahly has 

 been for a very "long time. This method of cultivation is de- 

 scribed by every early explorer and writer on Indian agriculture 

 and seems to have been the rule from the garden beds of the 

 Great Lakes region to the terraced mountain slopes of Peru. In 

 many instances as many as eight or ten plants were grown in a 

 single hill. This was the outgrowth of the Indian's limitations 

 in the way of implements and domesticable animals, and the 

 plant was well adapted to it. The method was adopted by civil- 

 ized man and is extensively employed, with but few modifica- 



If all the plants in a hill were synaemie and flowered at the 

 same time and the air were motionless, the chances for self-polli- 

 nation would vary inversely as the number of plants in a hill. 

 Tendencies toward protandry, coupled with slight differences in 

 the time of flowering of the individual plants of a hill, the pre- 

 valence of winds, and the proximity of other hills increase the 

 chances for cross-pollination. Growing the plants in hills also 

 discourages the production of suckers, thus reducing the number 

 of inflorescences on a single plant, and consequently the chances 

 for self-pollination. 



This massing of plants together in hills, and of hills together 

 in fields, is admittedly an artificial element of environment ; but 

 its possible evolutionary effect in the ages during which it has 



B Gates, H. R,, "Farm Practice in the Cultivation of Corn," U. S. Dept. 

 Agr. Bull. 320, 1916, pp. 19-21. 



