CYTOGENETICS AND EVOLUTION OF THE GRASS FAMILY 1 83 



tion and polyploidy to 10 different tetraploid species, all of which are 

 amphiploids, combining the characteristics of two different diploid species. 

 The most successful amphiploids have been derived from the most specialized 

 diploid species, A. squarrosa, A. umbellulata and A. caudata. 



Experiments of artificial hybridization and chromosome doubling carried 



Fig. 5. Map showing the natural distribution of the diploid species of Aegilops 

 and the hmits of the natural distribution of the tetraploids. Areas into which the 

 genus has been introduced by man in historical time are not included. {From 

 Kihara, 1954.) 



out by Sears and Kihara have synthesized counterparts of some of the natural 

 tetraploid species, thus reproducing under observation an important part of 

 the evolution of these grasses. 



The areas of geographic distribution of the diploids are smaller than those 

 of the tetraploids and occupy the center of the distributional area of the 

 complex as a whole (fig. 5). From two to four diploid species occur together 

 in parts of Asia Minor and western Iran, and the range of A. umbellulata, 

 the diploid which has entered into the ancestry of the largest number of 

 tetraploid species, overlaps that of most of the other diploid species. The 

 formation of new hybrids and amphiploids involving these species is, therefore, 



