UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



AGRICULTURAL SCIENCES 



Vol. 2, No. 5, pp. 191-204, plates 36-28 October 19, 1920 



/NEW vo;.. 

 -OTaNj 



INTERSPECIFIC HYBRIDS IN CREPIS ^''*<''*^'' 



I. CREPIS CAPILLARIS (L.) WALLR. X C. TECTORUM L. 



BY 

 EENEST B. BABCOCK and JULIUS L. COLLINS 



■ u 



Althoiigh the problem of the mechanism of heredity may be said 

 to have been solved by Morgan and others^ by means of the genetic 

 analysis of a species of flies, Drosophila melanogaster, there yet 

 remains the highly important question regarding the generality of 

 the conclu.sions based on the Drosophila data. As has been pointed 

 out by Morgan,- no method of determining the specific relation of 

 individual chromosomes to particular somatic characters appears more 

 promising than the study of hybrids between species. Especially is 

 this the case when the species possess low chromosome numbers. If 

 such species can be subjected to extensive genetic analysis so that the 

 factorial composition of each pair of chromosomes may be described 

 with some degree of exactness, and if fertile hybrids between such 

 species can be obtained so as to permit of breeding as well as of cyto- 

 logical investigations of the hybrid progeny, we should find here the 

 most promising material with which to test the generality of the 

 chromosome theory of heredity. 



Inasmuch as several species of Crepis were known to possess low 

 chromosome numbers, considerable attention has been given by the 

 writers^ to the genetic investigation of two of these species, viz., 

 Crepis capillaris (vircns)'^ and C. tectorum L., the results of which 



1 Morgan, T. H., Sturtevant, A. IT., Muller, U. J., and Bridges, C. B., The 

 Mechanism of Mendelian Heredity. New York, Holt, xiii + 262 pp., frontispiece, 

 and unnumbered diagrams. 1915. 



2 Morgan, T. H., The Physical Basis of Heredity. Philadelphia, Lippincott, 

 pp. 1-305, 117 illustrations. 1919. 



3 Babcock, E. B., "Crepis — a promising genus for genetic investigations." 

 ^-, Amer. Nat., vol. 54 (1920), pp. 270-276. 



Oi * Britten, James, and Eendle, A. B., "Notes on the 'List of British Seed 



^^ Plants.' " Jour. Bot., vol. 45 (1907), p. 102. 



