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University of California Publications in Agricultural Sciences [Vol. 7 



given an intermediate number of lobes in F^ generation and in F, 

 the progeny ranged from one parent type to the other. Out of the 

 250 Fo plants studied not one fully represented the grandparent types, 

 and on mathematical considerations there must be at least four factors 

 responsible for this condition. Shull (1918) in his work on the leaf 

 forms of the Shepherd 's Purse has formulated a two factor hypothesis, 

 the double dominant homozygote, the two single dominant homozygotes 

 and the double recessive, giving the four classes which he obtained. 

 With regard to the work on the length of the leaf, it has been found 

 that, as compared to the length, the breadth of a leaf is a much more 

 constant character as shown by table 6. The data for this table were 



TABLE 6 

 Showing Average Length and Width of Leaves in 100 Plants of Family 20.140 



obtained from a family of plants selected at random. This observation 

 is in accordance with the reports of some other investigators. More- 

 over, the length of a leaf is more markedly susceptible to environ- 

 mental influences and fluctuations due to modifications will profoundly 

 interfere with estimating the effects of recombinations. It is therefore 

 believed that races should be purified for the breadth factor rather 

 than for the length factors for facilitating studies in this direction. 

 During the progress of the work, several crosses were made between 

 strains of Crepis, and some of the strains were inbred. The result in 

 many cases was comparable to the results of inbreeding in corn. As 

 Collins (1920) has noted, plants of inbred strains may not put out 

 flowers at all, or if they do, very few of the heads set seed. Some of 

 these are viable and give rise to seedlings which may not thrive very 

 well unless they are given special care. They are not as strong as those 

 obtained from hybrid plants. When they have grown beyond the 

 seedling stage, they sometimes stay in the rosette stage much longer 

 than is usual and the vegetative period is consequently prolonged. One 

 strain remained in the rosette stage and produced no flowers although 

 it had been growing for over a year and a half. Other abnormalities 

 have also been noted, .such as vegetative proliferation and fasciation 

 of stems and peduncles. Often the flower heads are fasciated and 



