182 Gigantism in Primula sinensis 



Although not directly germane to the subject of gigantism it may 

 be recorded here that the form of inflorescence of the cultivated varieties 

 of P. sinensis appears also to be determined by the mode of distribution 

 of three factors in the zygote. 



Thus in the cross just described (Giant Pink x Lord Roberts Star) 

 the somewhat delicate and few-flowered type of inflorescence character- 

 istic of Lord Roberts Star disappears in the F^ generation and in the 

 Fa generation there are produced : 



212 non-" Roberts" inflorescence : 8 "Roberts": 

 which ratio points to the oonclusion that general type of inflorescence is 

 determined by three factors (XYZ) ; that the Lord Roberts Star type 

 which is patently more feeble than either the sinensis or stellata types 

 is produced in pure form only when the zygote has the constitution 

 xxyyzz ; and that Roberts-like inflorescences are also produced in 

 plants of the constitutions Xxyyzz and xXyyzz. 



If this be so then in 64 F2 plants there are to be expected : 



3 Roberts : 61 non-Roberts 

 and in 211 plants 99 „ : 2011 

 whereas 8 „ : 203 „ were found. 



The finer details of form of inflorescence, length of peduncle, length 

 of pedicel etc., appear also to be determined by Mendelian factors. The 

 evidence in support of this statement must be reserved for a further 

 communication, although the fact, that the Mendelian method may aid 

 the plant-breeder to trim up a plant to almost any desired form — to 

 straighten the leaves, to elongate the pedicels, to lower or heighten the 

 inflorescence — deserves to be brought to the attention of professional 

 plant-breeders. 



To return to the subject of gigantism : the hypothesis that this 

 phenomenon depends on not less than three factors drives us directly 

 to the conclusion that the classification of varieties of P. sinensis into 

 giant and non-giant forms is illusory. For it is a necessary corollary 

 to that hypothesis that the mode of distribution and combination of 

 these factors must be very different in the different races. In other 

 words the conclusion is inevitable that, as is notoriously the case in 

 other cultivated plants, P. sinensis must contain not only giant and 

 dwarf strains but also semi-giant races. Further the hypothesis 

 enables us to understand our failure to recognize, previous to Men- 

 delian experiment, the existence of such diverse races. For with 

 three factors concerned in the determination of stature the number of 



