60 RADIAL REPETITION. [introd. 



no evidence : it is therefore a fair presumption that they are 

 either rare or non-existent ; and that the peach-state and the 

 nectarine-state are thus positions of " Organic Stability," between 

 which the intermediate states, if they are chemical ami physical 

 possibilities, are positions of instability > 



These examples of Discontinuity in Substantive Variation 

 must suffice to illustrate the nature of the phenomena. It will be 

 seen that the matters touched on cover a wide range, and the 

 evidence relating to them must be considered separately and at 

 length. Such a consideration I hope in a future volume to 

 attempt. 



SECTION XI. 



Discontinuity in Meristic Variation : Examples. 



Inasmuch as the facts of Meristic Variation form the substance 

 of this volume, it is unnecessary in this place to do more than refer 

 to the manner in which they exhibit the phenomenon of Dis- 

 continuity. One or two instances must suffice to give some sug- 

 gestion of this subject, detailed consideration being reserved. 



Parts repeated meristically form commonly a series, which is 

 either radial or linear, or disposed in some other figure derived 

 from or compounded of these. For the purpose of this preliminary 

 treatment an instance of Discontinuous Variation in each of these 

 classes may be taken. 



1. Radial Series. 



\Variations in the number of petals of actinomorphic flowers 

 exhibit the Discontinuity of Meristic Variation in perhaps its 

 simplest form. 



Phenomena of precisely similar nature will hereafter be de- 

 scribed in animals, but such variations in flowers are so common 

 and so accessible that reference to them may with profit be made. 

 In Fig. 7 such an example is shewn. 



It represents a Tulip having the parts of the flower formed in 

 multiples of four, instead of in multiples of three as normally. 

 Variation of this kind may be seen in any field or hedgerow 1 . 



Meristic Variation is here presented in its greatest simplicity. 

 Such a case may well serve to illustrate some of the phenomena of 

 Discontinuity. 



1 For full literature and lists of cases see especially Masters, Vegetable 

 Teratology, s. v. Polyphylly. It is perhaps unnecessary to refer to the fact that 

 the numerical changes here spoken of are quite distinct from those which result 

 from an assumption by the members of one series or whorl of the form and 

 characters proper to other whorls. 



