236 University of California Publications in Agricultural Sciences [Vol. 7 



sizes of flowers which are practically identical (see East, 1921, p. 329) 

 and while casual observation leads me to believe that the number of 

 flowers per plant and the number of florets per head vary directly 

 with the size and shape of the plant, the diameter of the flower head 

 is not subject to influence by any one of these three factors and is 

 relatively stable, (See Stout, 1918.) The only factor that has been 

 found to influence the size of the flower heads is the moisture content 

 of the soil. The drier the soil the smaller the heads become. Here 

 the plants in pots have an advantage because the soil is never allowed 

 to become dry and the slight variations of moisture to which the plants 

 in pots are subject do not affect the diameter of the flower heads to 

 any appreciable extent. The results obtained from field plants are 

 strictly comparable among themselves, however, since all the strains 

 are subject to the same unfavorable environmental influences and as 

 such give results strictly comparable. 



SUMMARY AND CONCLUSIONS 



1. Crepis capUhiris has been found to be a valuable species for 

 genetic investigations because it is a wild plant which has not been 

 subjected to conscious selection by human agency. 



2. It can be cross-fertilized and the progeny derived from such 

 cross-fertilization is fertile inter se and gives viable seed. 



3. Several characters in the plant are constant and breed true when 

 the material has been purified to bring it into a homozygous condition 

 for the character in question. 



4. Continual selfing of the plant is followed by the usual symptoms 

 of such treatment in naturally' cross-fertilized species, resulting in 

 reduced vitality, arrested development at the rosette stage, formation 

 of many sterile flowers, few viable achenes, vegetative proliferation 

 and fasciation of the capitula and the stem. 



5. Three quantitative characters were studied in this plant : the 

 length of the leaf, the number of lobes in the leaves, and the diameter 

 of the flower heads. 



6. Length of leaf is a heritable character, but the environment 

 has a very great influence. The resulting fluctuating variability is 

 so great that although crosses have been made for studying the type 

 of inheritance, it is difficult to classify and segregate the F. progeny. 



7. In inheritance studies, width of leaf is a better index of leaf 

 size than length. 



