UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



AGRICULTURAL SCIENCES 



Vol. 2, No. 6, pp. 205-216, plates 39-41 November 23, 1920 



INBREEDING AND CROSSBREEDING IN 

 CREPIS CAPILLARIS (L.) WALLR. 



BY LIBRARY 



JULIUS L. COLLINS ^^ '*<*■ 



INTRODUCTION AND BRIEF DISCUSSION OF 

 INBREEDING EFFECTS 



It is well established that continued inbreeding within a strain 

 or race may produce results harmful to individuals of that race. It 

 is only in modern times, however, that a consistent explanation of 

 the causes of such results has been made. This explanation of the 

 problem has come through carefully planned and executed experi- 

 ments upon plants and animals and through a recognition of the 

 Mendelian laws of heredity. The most extensive and comprehensive 

 of these investigations is that with maize, started by East^ in 1905 

 and now being carried on by Jones, at the Connecticut Agricultural 

 Experiment Station. 



Inbreeding is now considered and used as a method by which the 

 hereditary constitution of the germ-plasm can be made evident. In- 

 breeding, as such, produces no evil results. The abnormal forms that 

 sometimes appear in inbred strains show up because the recessive genes 

 conditioning such forms are present in the germ-plasm. If no such 

 genes are present, no amount of inbreeding can produce them. 



The fact that inbreeding produces abnormal forms and reduction 

 of vigor in some species and not in others is due to a condition of 

 the germ-plasm. For example, no such results attend inbreeding in 

 self-fertilized crops like wheat and barley because in them self-fertil- 

 ization is the normal method of reproduction and such plants are 

 homozygous for all their genes, all the abnormal and weak plants 



1 East, E. M., and Jones, D. F., Inbreeding and Outbreeding, pp. 1-285, 46 

 illus., Philadelphia, Lippincott. 1919. 



