180 



Gigantism in Primula sinensis 



the floral habit of a plant may approach so nearly that of a giant as to 

 be recorded as a "doubtful giant" although, as shown by its progeny, 

 it is not pure for the giant character. 



TABLE VII. 



The Production of Giants hy the Crossing of Non^Giant Forms. 



1909 

 1910 



F,= 



1911 JF,= 



1912 F3 = 



Snow Drift x Snow King^ 

 22 plants : no giants recorded 



selfed 2 plants 

 51/1 = 17 plants : no giants 

 51/2 = 16 plants of which 1 = (? giant) (51/2/1) 

 selfed (? giant) and 4 non-giants 

 ' 5\j2j\ (from (2 giant) ^2)= 7 plants, viz. 5 non-giant, 2 giant 

 51/1 (from non-giant F2) = 13 

 51/H „ „ = 5 



511 M „ „ =14 



51IW „ „ =27 



- 59 plants : none giant 



II 



1909 

 1910 

 1911 

 1912 



Fi = 

 F2= 

 F.= 



Snow Drift x White Queen Star (Normal) 



9 plants, no giant 



8/2/2 r= 15 plants, no giant 



{8/2/11 =1 plant non-giant 

 8/2/2/11 = 9 plants, no giant 

 8/11 = 18 plants J 1 with giant flowers 

 t 1 ? giant 

 = 17 (? 16) non-giant : 1 (?2) giant 



It must therefore be assumed that combinations of the factors A, B, C 

 other than the combination AABBCC may give rise to giant-like forms. 



The assumption which appears to fit the facts most nearly is as 

 follows : Of the three factors A, B, C two, but not any two, must be 

 present in the homozygous state for the definite manifestation of 

 gigantism. Provided that the plant have the constitution AABB, it may 

 exhibit well-marked gigantism even though the third factor C be present 

 in the heterozygous condition. Thus the three factorial combinations 

 AABBCC, AABBCc, AABBcC may all produce giant-like plants, albeit 

 the homozygous giant is recognizably more gigantic than the hetero- 

 zygous giants. 



The genetical behaviour of the "doubtful" giant 51/2/1 (Table VII, I) 

 demonstrates that it is not pure to gigantism. If there be ascribed to 

 it a constitution AABBCc, it should yield an F3 of 



lAABBCC : 2 { ^^^^^^ : lAABBcc. 

 (AABBCc 



1 Snow King has flowers of fair size (stellata type) and should perhaps be classed as a 

 semi-giant. 



