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University of California Pvblicaiions in Agricultural Sciences [Vol. 7 



to a maximum of 4 mm., but usually it ranpred betAveen 2 mm. and 

 3 mm., and more often reached the lower limit. Tf at this stage 

 tlic land wa.s irrigated, the measurements taken the next day in- 

 variably showed a rise. The following data taken on plants of the 

 same population both before and after irrigation illustrate this point. 



-Culture Hsu 20.1- 



There is an average difference of 0.21 cm. or approximately 2 mm. 



A Cross Involving Difference in Head Size 



This particular work was started in the summer of 1921 and was 

 carried only to the F^ stage. Two strains were chosen, one having a 

 diameter ranging from 17 to 25 mm., and the other from 21 to 36 mm. 

 These races had undergone a preliminary purification for size of flower 

 head. The F^ was intermediate and the mean of the F^ population 

 was closer to the mean of the smaller parent than that of the larger 

 parent. The data that have been secured on this work are given in 

 table 5. Other crosses have given similar results, but as the parent 

 strains did not differ in any marked degree, the F^ obtained shows 

 about the same size of head diameter. 



