250 University of California Publications in Agricultural Sciences [Vol. 2 



Material and Methods 



The genus Crcpis, containing over 150 species, is a member of the 

 Ciehorieae or chicory tribe of the Compositae, the best known related 

 genera being Hieracium, Lactuca, Sonchus, and Taraxacum. 



Crepis capiUaris (L.) Wallr. is an annual, but under certain cir- 

 cumstances may assume the biennial habit. The plant first produces 

 a rosette of radical leaves which have been found to vary in different 

 plants from entire to bipinnately compound. The stem is usually 

 single with paniculate branching above and varies from a few inches 

 to four feet in height, largely depending upon conditions of growth. 

 The cauline leaves are sessile, amplexicaul, clasping, the lower ones 

 more or less lobed or pinnatifid, while the upper ones are slender and 

 entire. The underside of the midribs of the rosette leaves, and to 

 some extent the upper side, and the lower cauline leaves are more or 

 less covered with bristly hairs. In many, but not all, plants the 

 involucre and peduncle are glandular pubescent in addition to the 

 fine gra.y tomentum w^hich is always present. The brown terete 

 achenes vary in length from 2 to 3 mm., are attenuate at both apex 

 and base, and usually lO-ribbed. The yellow flower heads vary from 

 17 to 25 mm. in diameter. 



During the course of the investigations, achenes of C. capiUaris 

 have been obtained from many localities of the temperate and sub- 

 tropical zones of both the old and the new world. The species is 

 apparently a native of Europe, but is now disseminated throughout 

 the world. 



The methods used in growing experimental cultures of Crepis 

 have been previously published (Collins, 1922). 



In presenting data from hybrid populations, the degree of corre- 

 spondence of observed with calculated distribution has been deter- 

 mined by use of tables of probable errors of Mendelian ratios prepared 

 by the Department of Plant Breeding of Cornell University. In the 



case of some dihybrid populations the method suggested by Harris 



(o c)^ 



(1912) has been used. This formula is X^ = '2,- , in which o 



is the observed frequency of any class, c, the calculated frequency for 



that class, and 2 indicates that all the values of the type ; are 



added together. From Elderton V tables for calculating the goodness 

 of fit, the probability for the chance occurrence of the deviations in 

 the observed classes has been obtained from the calculated value of X^. 



3 Given in Pearson, K., Tables for Statisticians and Biometricians, Cambridge 

 Univ. Press, 1914. 



