378 University of California Puhlications in Agricultural Sciences [Vol. 2 



All these consequences of triploidy, whether direct or indirect, 

 make it an important phenomenon and one that should be kept in 

 mind not only in theoretical work but also in practical breedinf^. It 

 is sufficient here to mention the important services of trisomic and 

 polyploid ratios in the task of localizing: genes, the important results 

 of investigations on genie balance and sex determination, etc. The 

 value of seedless fruits and the superiority of triploid flowering 

 bulbous plants give good illustrations of the practical importance of 

 triploidy. Chromosomal variation also probably accounts for the 

 origin of many new ornamental and commercial varieties. 



This paper contains the first report on investigations carried on 

 during the period 1926-1928. The investigations were conducted 

 mainly in the laboratories and experimental grounds of the Timiria- 

 sev Federal Institute of Scientific Research and of the Comakademy 

 in Moscow; and were completed at the Division of Genetics, Univer- 

 sity of California, under a fellowship of the International Education 

 Board, New York. 



Acknowledgments 



During the course of the w^ork the writer had the excellent assist- 

 ance of Miss Gerassimova of Moscow, which it is a pleasure to 

 acknowledge here. The data obtained by Miss Gerassimova will be 

 mentioned in the course of this paper. The writer is especially glad 

 to express his gratitude to Professor E. B. Babcock and Professor 

 R. E. Clausen, of the University of California, for many valuable 

 suggestions and for active interest in the work. 



OCCURRENCE, MORPHOLOGY, AND CYTOLOGY OF 



TRIPLOIDS 



In a study of extensive material of Crepis several triploid plants, 

 Crepis capillaris (L.) Wallr., C. dioscoridis L., and C. tectorum L., 

 were found, as well as other chromosomal variations. A preliminary 

 note on polyploidy in Crepis (Navashin, 1925) and general observa- 

 tions regarding the cytology and morphology of polyploids have 

 already been published (Navashin, 1926). It has been shown that 

 in populations of C. capillaris and C. tectorum triploid individuals 

 are frequent, being sometimes present to the extent of one per cent of 

 the total number of plants. Such a high degree of occurrence can- 

 not be without some influence on the genetic behavior of the species 

 involved. 



