18 HEREDITY [ch. 



would be obtained having two maxima, one near 62 

 and another near 68. Yet the stature might be a 

 definite sexual character, and hence essentially as 

 discontinuous as the sexes themselves. This distinc- 

 tion between continuous and discontinuous variation 

 may seem unimportant in itself, but when its in- 

 heritance is considered the distinction becomes of the 

 first importance. 



Clearer examples of discontinuous variation are 

 given by such characters as colour, or by organs 

 which are repeated in series, such as vertebrae and 

 ribs, the segments of a worm or the petals of a 

 flower. When variation occurs in this latter group 

 it is generally complete, so that the different forms 

 are visibly discontinuous. In the case of colour in 

 the skin or hair in animals, or petals of flowers, 

 discontinuity is sometimes less apparent, and grading 

 frequently occurs, but even in apparently graded 

 cases the inheritance of the character may often 

 reveal discontinuity. For example, a piebald animal 

 might be thought to be intermediate between the 

 fully-coloured and albino (white with no pigment), 

 but breeding tests would at once show that piebald- 

 ness was an independent character, which cannot be 

 regarded as in any sense intermediate between the 

 other two conditions except in general appearance. 

 The same applies to such cases as the ' silver ' cat or 

 rabbit, or the pale purple sweet-pea ; the cause of 



