[THOMPSON] RIPENING PERIODS IN WHEAT «7 



6. Summary. 



1 The results are reported of crosses between many pairs of 

 wheat varieties differing by many degrees in regard to the length ot 

 the ripening and heading periods. Crosses between parents diftenng 

 only slightly were made over the whole range of variation, and crosses 

 were also made involving successively greater parental differences. 



2 The Fi plants matured with the late parent. This appears 

 to be a case not of dominance but of postponement of the hereditary 

 maturation period due to vigor of crossing though there are difficulties 

 in this interpretation. 



3 The F, plants formed regular curves of probability with inter- 

 mediate means. In most cases the variation extended from below 

 the mean of the lower parent to above the mean of the higher parent. 

 Where the parents differed only slightly the parental extremes were 

 sometimes exceeded. Where the parents differed greatly the parental 

 extremes were not always reached though the parental means were 

 usually exceeded. 



4 Interpreting the results on the basis of the multiple determiner 

 hypothesis of blending, the sum of the differences between each success- 

 ive pair of parents seems to be much greater than it should be on the 

 evidence of direct crosses. This hypothesis therefore fails to explain 

 satisfactorily the results as a whole though it may explain satisfactorily 

 the results of each individual cross. 



5 Eariiness can be combined with other desirable qualities by 

 Mendelian methods, though it is necessary to raise very large numbers 

 of plants because the great majority are intermediate. 



7. Literature Cited. 



1. Castle, W. E., 1916. 



New Light on Blending and Mendelian Inheritance. Amer. Nat. Vil. L. 

 No. 594, pp. 321-334. 



2. HosHiNO, Yuso, 1915. 



On the inheritance of the Flowering Time in Peas and Rice. Jour. Loi. 

 Ag. Tohoku Imp. Univ., Sapporo, Japan, 6, Pt. 9, pp. 229-288. 



3. Leake, H. M., 1911. 



Studies in Indian Cotton. Journal Genetics. Vol. 1., Pp. 205-272. 



4. Tschermak, E. v., 1911. . 



Ueber die Verebung der Blutezeit bei Erbsen. Verh. Naturf. Verem, 

 Brunn, Vol. 49. 



