F. Kebble 179 



The Fi plants yielded an F^ generation which in one ease consisted 

 of 54 non-giants and no giants and in another case was composed of 

 67 plants of which one was a giant. 



The ratio 66 non-giant : 1 giant suggests the further hypothesis 

 that gigantism depends for its expression on three factors. Let it be 

 assumed that a giant differs from a Normal Pink Stellata in the possession 

 of at least three factors, which factors are either different in nature or 

 — and more probably^similar in nature and of different distribution 

 in the germ-plasm. Then when the giant of constitution AABBCC is 

 crossed with a form which by virtue of its size and habit may be 

 assumed to lack all three factors the result is an F-^, the members of 

 which are heterozygous for all three factors. Thus : 



AABBCC X aabbcc, 

 Fi = AaBbCc non-giant, 



and F. = lAABBCC : 63 plants of other constitutions, 



= 1 indubitable giant : 63 other plants, 



none of which appears as a giant when viewed beside the pure dominant 

 giant form. 



Results which point to ratios of this order are exhibited in Table V. 

 Thus in No. 120/07 the F„ of the cross Royal White x Pink Stellata 

 consists of 67 plants of which 66 are non-giant and 1 is giant. In 

 another F^ family of the same origin no giant appeared among 54 plants. 



The case of Snow Drift x Snow King (Table VII, I) is similar and 

 of interest in another direction also, inasmuch as it affords an example 

 of the origin of a giant race as the result of crossing two non-giant 

 varieties. The F„ generation consists of 33 plants of which one was 

 recorded as a "doubtful giant" (51/2/1). This plant yielded an F, 

 consisting of seven plants of which five are non-giant and two are 

 giants. Four of the non-giant F„ plants yielded F^ families which 

 together contained 59 plants none of which are giants. 



The results of this experiment and those of the experiments described 

 previously conform with the requirements of the hypothesis that floral 

 gigantism is determined by three factors, all of which must be present 

 in the homozygous condition for the phenomenon to be exhibited. 



The results now to be described require a slight modification, or 

 rather extension, of this hypothesis. 



As mentioned already the " doubtful giant " (51/2/1) obtained in 

 the F.2 of the cross Snow Drift x Snow King (Table VII, I) yields an 

 F3 consisting of 5 non-giants and two giants. Whence it follows that 



