Basis of Systematic Relationship 73 



Some pangens represent characters which usually de- 

 velop only in quite definite organs. If these happen to- 

 predominate in the wrong place we get the phenomena of 

 metamorphosis. 46 If, for example, the pangens which 

 determine the peculiarities of the petals develop in the 

 bracts the petalody of the bracts takes place. 



Other pangens represent qualities which may appear 

 in many or in all members of the plant. And therein lies 

 doubtless the reason that such characters are so very 

 often equally strongly or feebly developed in all of 

 those members. Thus the red coloring matter of the 

 white-flowered varieties of red species is most frequently 

 also lacking in the stem and foliage, and plants with 

 variegated leaves not infrequently bear variegated fruit. 



Phenomena of correlative variability, when not of 

 purely historical nature, i. e., if not originated by simul- 

 taneous accumulation of two independent qualities, find 

 their explanation in the union of the pangens into groups. 



Systematic relationship is based on the possession of 

 like pangens. The number of identical pangens in two 

 species is the true measure of their relationship. The 

 work of the systematist should be to make the applica- 

 tion of this measure possible experimentally, by finding 

 the limits of the individual hereditary characters. Sys- 

 tematic difference is due to the possession of unlike pan- 

 gens. 



According to pangenesis, there may be two kinds of 

 variability. These are differentiated in the following 

 manner by Darwin. 47 In the first place the pangens 

 present may vary in their relative number, some may in- 

 crease, others may decrease or disappear almost entirely, 



46 Darwin, C Loc. cit. 2: 387. 

 "Loc. cit. p. 390. 



