274 Heredity and Repetition of Parts [ch. 



heterozygous parent^, we cannot say with any confidence ; 

 but in considering the significance of the phenomenon of 

 bud-sporting that special problem is of subordinate conse- 

 quence, for in either event there must have been a process 

 of allelomorphic segregation at some somatic division. 



In our Sweet Pea cultivations a phenomenon precisely 

 comparable occurred in two individuals of similar breeding. 

 The plants were purples of the dark type with purple 

 wings (Plate III, fig. 7), and were heterozygous for the 

 blue factor, B, After a few hot days they stopped flowering. 

 Then wet weather succeeded and much secondary growth 

 was made, young iiowering shoots springing in the axils of 

 the older stems. On two individuals one of these young 

 shoots bore a flower of the red, or Miss Hunt type 

 (Plate III, fig. 8), showing that the factor B had been 

 omitted in one of the cell-divisions by which they were 

 formed. 



The Differentiation of Repeated Parts compared 

 with Segregation. 



Such facts raise a theoretical question of fundamental 

 importance. If upon the same individual, parts may as an 

 abnormal occurrence present the same differentiation which 

 is known to be characteristic of dominant and recessive, 

 may not the differentiation normally existing between re- 

 peated parts of the same individual be a phenomenon of 

 segregation ? Why, for instance, may not the differentiation 

 normally existing between petal and leaf, or between the 

 appendages of arthropods, or any other meristically repeated 

 parts, be due to a segregation acting amongst somatic parts 

 as amongst gametes ? Evidently, as morphologists have 

 often argued, the relationship between individuals is com- 

 parable to that existing between repeated parts. By tracing 

 the comparison in one direction we reach the fact that 

 hereditary resemblance is the same phenomenon as that y 

 which we elsewhere know as symmetry : for if a cell divides 

 into two similar halves, and each half undergoes similar 



* Comparable, for instance, with gynandromorphous insects, half male, 

 half female ; or with white flowers showing a well-defined patch of some 

 coloured variety. 



