256 University of California Publications in Agricultural Sciences [\^ol. 2 



LEAF VARIATIONS 



From the very first acquaintance with C. capillaris, the different 

 forms in the rosette leaves constituted the most striking and out- 

 standing; variations. They have proved equally as difficult to study 

 genetically, due, first, to the difficulty in evaluating non-genetic 

 variability' resulting from age of plant and from environmental causes, 

 and, second, to the complex heterozygotic nature of the material in 

 the wild condition. Sears (1921) found in Taraxacum that the degree 

 of leaf dissection is correlated with the age of a given rosette. The 

 leaves of a very young rosette are almost entire, becoming progres- 

 sively more dissected as the rosette becomes older. Stork (1920), 

 also working with Taraxacum, found that in very young plants 

 the rosette leaves ranged in form from entire to deeply pinnatifid- 

 runcinate, but became more, instead of less uniform, as they grew 

 older. Neither condition can therefore be taken as typical for that 

 species. In Crepis, a closely related genus, there is a more regular 

 sequence of development of leaf shape for a particular rosette. The 

 juvenile leaves are usually entire or nearly so, and assume their 

 typical forms gradually as the plant reaches the mature rosette stage 

 just preceding the appearance of the flowering stalk. At this time 

 there exist individual differences which range in form from entire 

 to deeply pinnatifid or compound pinnatifid. That these differences 

 are genetic is shown, first, by the fact that inbreeding has resulted 

 in the isolation of races of the different types which breed true when 

 grown side by side under similar conditions, thus to a large degree 

 eliminating the effect of the non-genetic factors, and, second, that 

 the forms when crossed give a fairly uniform F^ and segregate into 

 the parental and Fj forms in the second generation. 



By means of inbreeding and selection, a number of distinctive, 

 uniform races have been obtained in almost homozygous condition. 

 A brief description of each is given below. 



VIEIDIS 

 Plate 45, figure 1 



This form was isolated in 1919 from the Eureka (California) 

 stock. The rosettes are small, 4 to 10 inches in diameter. The leaves 

 are deeply lobed or pinnately parted, and are lacking in anthocyanin. 



