CYTOGENETICS AND EVOLUTION OF THE GRASS FAMILY 1 85 



part in south central Asia, they occupy very Hmited areas. Each diploid 

 type is markedly distinct from other diploids in outward appearance and 

 is rather constant. Some of them differ widely from each other in their 

 climatic preferences, and together they represent all the types of climatic 

 tolerance found in Dactylis. In addition to the forest-loving D. aschersoniana, 



Fig. 6. Map showing the natural distribution of the diploid subspecies of Dactylis 

 and the probable hmits of the tetraploids before they became spread throughout the 

 temperate regions of the world by man. 



which has a close diploid counterpart in the forests of the Himalaya and 

 western China, and the steppe-inhabiting D. woronouni, the known diploids 

 include three native to restricted areas in the Mediterranean region, with its 

 mild wet winters and dry, hot summers; one found in the equable climate of 

 the Atlantic coast of Portugal; one adapted to high montane or subalpine 

 conditions in the Sierra Nevada of southern Spain; and finally a peculiar 

 diploid, D. smithii, endemic to the Canary Islands, where it grows in the 

 subtropical belt, in the zone of banana cultivation (fig. 6). 



Although these diploids are sharply distinct morphologically, they are 

 closely related genetically. They are easily intercrossed, and with a few excep- 

 tions the artificial hybrids between them are vigorous, fertile, and have per- 



