172 TJniversity of California Puhlications in Botany [Vol. 5 



rows and cultivated just as in the cultures of the previous two 

 years. The figures given are most important, however, in that 

 they show that with an increase in size and fluctuation due to 

 more favorable cultural conditions no intergrading of one variety 

 into another takes place and that on the contrary the three 

 varieties are even better distinguished from one another in corolla 

 diameter than before. 



The following Fo hybrid generations have been raised during 

 1912— F, of the crosses III$XlIcf, I$XlId', H^Xlll(^ and 

 IIIJXlcT- Over five thousand measurements of corolla diameter 

 have been made upon three of these F. generations while the 

 fourth is at present just coming into flower. From 15 to 18 

 plants in each group were brought to maturity and their flowers 

 measured. 



The actual results (calculation of the means and coefficients 

 of variation) of these measurements have not as yet been com- 

 pletely determined but the general trend of the results is suf- 

 ficiently clear to make this preliminary account of them possible. 

 Contrary to the expectation expressed the variation in corolla 

 diameter in F, appears to be more or less greatly increased as 

 compared with that noted in Fj. Thus, whereas in the Fj plants 

 the range of variation was two or three times as great as that of 

 the parents, in Fo the minimum range of variation is always over 

 twice and the maximum range five or six times as great as that 

 of the parents in 1910 and 1911. In the case of Fj of the cross 

 I^XIIJ* certain plants show a range of variation in corolla 

 diameter from a flower 2 mm. smaller than the smallest flower 

 ever measured on Variety II to a flower 3 mm. larger than the 

 largest flower borne by Variety I in 1912 and 7 mm. larger than 

 the largest flower produced by Variety I in 1910 and 1911. An 

 increase in vigor where size and form characters are being dealt 

 Avith, is often to be expected in F^ yet this common result of 

 hybridization was not observed in the F^ previously reported 

 upon (cf. also. East and Hayes, 1912). Certain plants in the 

 Fo generation of this same cross, however, exhibit as small ranges 

 of variation as do the parental varieties this year (1912) and 

 they are always the plants which bear the largest flowers. F, 

 individuals of the cross III^XlIJ* similarly exhibit an extended 



