74 INTROGRESSIVE HYBRIDIZATION 



For the great bulk of our cultivated plants it will be diffi- 

 cult, or impossible, to bring together the data on wild pop- 

 ulations, weed populations, and geographical distribution 

 which will permit us to demonstrate step by step these com- 

 plicated processes of domestication. The major areas of 

 domestication (Asia Minor, Southeastern Asia) are difficult 

 of access to most students. However, there are a few cul- 

 tivated plants and weeds whose histories are more accessible, 

 and for a few of them data on introgression are already be- 

 ginning to appear. Of these the common cultivated sun- 

 flower, Helianthus annuus, is in a class by itself in the degree 

 to which we may some day hope to demonstrate in detail 

 the steps by which it became a cultivated plant and a weed. 

 It was domesticated in pre-Columbian times within the 

 boundaries of the present United States. A considerable 

 amount of prehistoric remains from archaeological sites are 

 already available in museums. Its wild progenitors are still 

 to be found in the United States in the west, south, and 

 southwest. Heiser has already (1947a, 19476, 1949) made a 

 promising beginning at unraveling the story of its domestica- 

 tion. Though, in comparison with the great world crops 

 such as rice, wheat, and maize, the history of the sunflower 

 is a relatively simple one, it is so complicated that a decade 

 or so of intensive work will be needed to establish the main 

 points. As the story takes shape with such data as are now 

 available, it is about as follows: 



If we use the expression Helianthus annuus in its widest 

 sense, there can at present be recognized the following dif- 

 ferent entities : 



A. Cultivated large-headed varieties (chiefly monocephalic), grown 

 for their large, oily seeds. 



B. Large-headed and small-headed varieties grown for ornament. 



C. Weeds of the Great Plains and adjacent prairies, oftentimes 

 growing in corn fields, gardens, etc. 



D. A second set of weeds, distinct from the preceding, limited to 

 trash heaps, railroad yards, and the like, typical "camp followers." 



E. A third set of weeds in the irrigated valleys of the far west. 



