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University of California Puhlications in Agricultural Sciences [Vol. 



SO obtained in a comparative study like this. The larger figure of 



each set was considered the more accurate measurement and hence 



was used to secure the 'corrected' totals and averages which appear in 



table 3. 



TABLE 3 



Measurement Data for Nineteen Species of Crepis 



Species 



C. capillaris 



C. neglecta 



C. setosa 



C. parviflora 



C. hursifolia 



C. aurea 



C. aspera 



C. alpina 



taraxacifolia.. 



tectorum 



hlattarioides . . 



japonica " 



foetida 



C. bidbosa 



C. rubra 



C. dioscoridis 



C. sieberi " 



C. pulchra 



C. sibirica 



Corrected average for individual chromosomes 



8.6 



a Averages from less than ten figures. 



The reliability of such measurements and the evidence for the 

 constancy of specific individuality have been further corroborated by 

 a study of chromosome measurements of the Fi's of two species-hybrids, 

 setosa X tectorum (fig. 1) and setosaXdioscoridis (fig. 2).^ It will be 

 noted from table 3 that all three species involved have four pairs and 

 that the chromosome sizes are far more different in the two latter than 

 in the two former species. In both F/s, however, it was possible to 

 determine the source of the chromosomes by means of measurement 

 data, and this was facilitated by the peculiar semidetached tip of the 

 longest chromosome of setosa (fig. 3), by which it may usually be identi- 

 fied. Since only one member of a set is present in each Fi figure, it 

 seemed best to compare the averages for the F/s with the uncorrected 

 averages for the species involved. The results are tabulated l^elow: 



' For the use of these hybrids and the data on hybridization given below, I am 

 indebted to Dr. J. L. Collins of this laboratory. 



