126 White. 



characters in heredity, but the phenomena are easily understood and 

 more simply expressed when one can work with progeny, the male and 

 female parentage of which is contained within the same plant. Under 

 the conditions above mentioned, an F2 population such as (396 X 301) 

 — 12 may contain: — 



AA segregates resembling AA plants of Xi standard, 



AA „ „ Aa „ „ „ „ 



AA „ very nearly as normal as those aa plants of Xi 



standard which have two or three abnormal flowers. 

 AA segregates which have numerous new modifications in the 

 expression of the factor. 

 Such an Fg may also contain: 



Aa segregates resembling AA plants of Xi standard, 

 Aa „ „ Aa „ „ „ „ 



Aa „ „ aa „ „ „ „ 



Aa „ with many new modifications. 



One can readily see from this illustration the confusion which would 

 ensue in attempting to classify such an Fo progeny. The study of 

 this factor A and its expression in the „soma" under differing geno- 

 typical conditions is exceedingly complicated because it is capable of 

 expressing itself as a modification in so many of the important plant 

 organs. The study of a color character is much simpler, as I shall 

 soon indicate. 



16. Dominance and recessiveness, being regarded as characteristics 

 of the environment (both genotj^ical and external) are expected to 

 show a large degree of variation in a series of crosses such as the 

 present investigation involves. A study of the Fi generation of four 

 very distinct species crosses and three fairly distinct varietal crosses 

 with the abnormal race (300—309) has fulfilled these expectations. All 

 the species and varieties are normal as regards fasciation, except 324 

 and perhaps to a slight degree 396. When crossed with the abnormal 

 (300 — 309) race, if other factors did not produce modifying effects, the 

 Fl plants from these different combinations should all show the same 

 degree of dominance and recessiveness. Such is not the case, however; 

 Fl plants of 301 X 373, etc. are the most normal, followed by 353 X 301, 

 301 X 353, 301 X 396, 303 X 327 in the order named, through to 

 332 X 301 or 332 X 303, 304 X 402, and 324 X 301, wliich are the most 

 abnormal. (Consult Tables 6 — 12.) The species crosses were all sterile. 

 The F2 generation of all the varietal crosses further substantiated this 



