218 University of California Putlications in Agricultural Sciences [Vol. 7 



OBJECTS AND AIMS 



The genus Crepis, comprising over 150 species, belongs to the 

 tribe Cichorieae of the natural order Compositae, and is closely related 

 to the genus Hieracnim. The species, C. capillaris, so far as known, 

 has not been brought under cultivation, but grows as a wild plant 

 in widely separated parts of the world. This species can be easily 

 propagated and the plants are self-fertile so that investigations may 

 be carried on with inbred strains. Furthermore, the F^ and F^ 

 generations from varietal crosses are fertile when crossed mter se, 

 and the species has a very low number of chromosomes. Hence as 

 Babcock (1920) pointed out, the advantages of the genus for genetic 

 investigation are many. Previous to that, some work had been done 

 on the cytological side, notably by Rosenberg (1909-1918), who de- 

 termined the number of chromosomes, Beer (1912), Miss Digby (1914) 

 and de Smet (1914). De Smet has given excellent illustrations of the 

 various stages of nuclear division. Other species of Crepis have been 

 studied by Rosenberg (1909-1918) and Juel (1905) ; interspecific 

 crosses between C. capillaris and C. tectorum have been reported by 

 Babcock and Collins (1920). The achenes of C. capillaris germinate 

 easily after a short period of rest and a very large percentage is 

 viable. The plant first develops a rosette and finally the central axis 

 elongates and terminates in an inflorescence ; but under unfavorable 

 conditions it may remain indefinitely in the rosette stage. The plant 

 is strictly annual, however, and dies after once flowering. Plate 43 

 illustrates typical plants when the inflorescence has developed and 

 growth has practically ended. 



The present investigation has to do specifically with differences in 

 the length of the radical leaves, in the number of lobes on the radical 

 leaves, and in the diameter of the flower heads. The aim was to deter- 

 mine whether these differences were inherited and to locate the factors 

 responsible for the genetic variations as distinct from modifications 

 due to the environment. In the case of the inheritance of morphologi- 

 cal characters in the leaf, the action of the environment had to be 

 taken into consideration, and in the case of the flowers, the action of 

 the environment in addition to the age of the plant and the position 

 of the capitulum upon the plant had to be evaluated before the true 

 genetic variations could be determined. The work has been carried on 



