46 Preliminary Deductions [ch. 



Cyclamen) are recessive to the paler and more commonplace 

 tmts^. 



Though in the case of colours in plants which are clue 

 to the development of pigmented sap, albinos are recessive 

 to the coloured types, the yellow or cream colour due to 

 the presence of yellow ch7^omoplasts is recessive to the 

 colourless condition of the chromoplasts. Hence we find, 

 what at first seems paradoxical, that white flowers are 

 dominant over cream-coloured fiowers. Yellow dependent 

 on sap-Q.o\o\xx is dominant to the corresponding white. 



With regard to the behaviour of black pigment, which 

 might naturally be supposed to have similar genetic pro- 

 perties in the various animals, no quite satisfactory general 

 rule can be laid down. The presence of black pigment is 

 commonly dominant to the absence of black, as in the race- 

 horse, where chestnut, namely the absence of black ''points" 

 is recessive to the presence of such "points" as in bays and 

 browns. Most cases, however, such as that of the mouse, 

 and other animals in which black pigment exists intimately 

 mixed with other pigments are not so simple as this and 

 involve special problems. In so far as the features of those 

 cases can be expressed in the simple terminology hitherto 

 used, these blacks must be classed as recessive to the normal 

 colours. Further particulars will be given in the chapters on 

 Colour. 



P7^eliminary Deditctions from Mendelian Phenomena. 



It will be observed that animals and plants, as such, 

 do not show any difference in their manner of heredity. 

 Inheritance on simple Mendelian lines may be followed 

 by characters of very diverse kinds, such as height, shape, 

 chemical constitution, colour, and several structural features. 

 In view of such a list the important question arises whether 

 there is any distinct category or class of characters to which 

 the Mendelian system does not apply. Various possible 

 limitations may be discovered when the phenomena have 

 been more fully examined, but it may be stated at once 

 that no such class of characters has hitherto been identified. 



* In Antirrhmum Miss Wheldale finds that the deeper magentas are 

 recessive to the ordinary magentas, but in the crhnson-rid series the paler 

 are recessive to the deeper tints. 



