seem to account very well for the range of chromosome numbers in 

 Crepis (Babcock, 1947) especially since interspecific hybrids between 

 species with n = 4 and n = 3 show the latter to have a chromosome 

 partially homologous to two in the former. There is also a good deal of 



Figure 8-7. Photomicrograph of Ring of 12 Chromosomes in Rhoeo 

 discolor Produced as the Result of Multiple Translocation. (From Darlington, 

 C. D. and LaCour. L. F., 1960. "The Handling of Chromosomes," 3rd ed., 

 George Allen & Unwin. Ltd., London, England, Plate XVIL) 



evidence that similar translocations have played a phylogenetic role in 

 many animals, especially in grasshoppers, some Diptera, and probably 

 in certain beetles such as the weevils (Smith, 1956). Indeed, much of 

 the diflference in basic chromosome number between related species, so 

 conspicuous in many animal groups, may ultimately be explained by 

 such "whole arm" exchange. 



CYTOGENETICS / 187 



