CH. xv] Nature of Units 267 



The conception of dominant characters as each due 

 to the presence of something which is absent from the corre- 

 sponding recessive may prove of use as assisting towards 

 the identification of these problematical bodies. To most 

 of the cases of allelomorphism between characters yet 

 detected, this method of representation may be very readily 

 applied. The round seed of peas, or of maize, is one which 

 contains something possessing the power of turning most of 

 the reserve-materials into starch. If the dominant factor 

 endowed with this power is absent, much of the sugar 

 remains sugar, and the seed wrinkles on ripening. The 

 actual physiological processes involved are doubtless more 

 complex than this, but there is no mistaking the essential 

 nature of the distinction between the round and the wrinkled 

 seed. So also it is easy to understand that an albino is an 

 organism from which a ferment responsible for the pro- 

 duction of colour has been omitted. No great strain is put 

 on this hypothesis of dominance even by the suggestion 

 that the production of hairs on the leaves of a Stock, or of 

 the disposition to go broody in a hen, may be directly 

 caused by specific substances, for it would not be difficult to 

 adduce pathological parallels for the production of bodily 

 and mental changes such as these in cases where the change 

 is plainly the work of a specific poison. Again it is easy to 

 imagine that the presence or absence of a ferment can confer 

 a greater power of resistance to the attack of a fungus. I 

 suppose also that the dominant whites met with in some 

 animals and plants may reasonably be represented as 

 organisms possessing a substance which has the power of 

 suppressing the development of pigment, whether by pre- 

 venting its excretion or by destroying it when formed. 



On the other hand it must be admitted that in appli- 

 cation to those examples in which the dominant factor 

 operates by inducing or suppressing the division of a certain 

 organ, the analogy with ferment-action is more difficult to 

 maintain. The double comb of fowls is nevertheless a 

 single comb made bifid by the addition of a dominant 

 factor. To suppose also that the suppression of a phalanx 

 in the digits of a brachydactylous man, or the development 

 of a rabbit's fur in the normal and not in the Angora manner 

 is thus decided by a specific substance, is to contemplate a 



