134 A Defence of Mendel' 's 



question cannot breed true even after successive selections, 

 but constantly break up into the same series of forms*. 



This conception of the "mule" form, or "hybrid- 

 character" as Mendel called it, though undeveloped, is 

 perfectly clear in his work. He says that the dominant 

 character may have two significations, it may be either a 

 parental character or a hybrid-character, and it must be 

 differentiated according as it appears in the one capacity 

 or the other. He does not regard the character displayed 

 by the hybrid, whether dominant or other, as a thing 

 inherited from or transmitted by the pure parent at all, but 

 as the peculiar function or property of the hybrid. When 

 this conception has been fully understood and appreciated 

 in all its bearings it will be found to be hardly less fruitful 

 than that of the purity of the germ-cells. 



The two parents are two let us say substances! 

 represented by corresponding gametes. These gametes 

 unite to form a new "substance" -the cross-bred zygote. 

 This has its own properties and structure, just as a chemical 

 compound has, and the properties of this new " substance " 

 are not more strictly traceable to, or " inherited ;: from, 

 those of the two parents than are those of a new chemical 

 compound "inherited" from those of the component 

 elements. If the case be one in which the gametes are 

 pure, the new " substance " is not represented by them, 

 but the compound is again dissociated into its components, 

 each of which is separately represented by gametes. 



f It will be understood that a " mule " form is quite distinct from 

 what is generally described as a " blend." One certain criterion of 

 the "mule" form is the fact that it cannot be fixed, see p. 25. 

 There is little doubt that Laxtou had such a " mule " form when he 

 speaks of "the remarkably fine but unfixable pea, Evolution." J. R. 

 Hort. Soc. xn. 1890, p. 37 (v. infra). 



t Using the word metaphorically. 



