MENDELISM AND OTHER METIIOPS OK DESCENT 2 23 



The degenerative nature of many valuable variations of 

 domesticated plants and animals is well known, and also their 

 generally recessive status. It might, therefore, be worth while 

 to take into account in experiments with plants this means of 

 bringing recessive characters into expression by the self-fertili- 

 zation of the perjugate individuals of crosses from which desir- 

 able variations are desired. 



Numerous analogies between hybrids and mutative new varia- 

 tions have been described and discussed in other places, but 

 the present indications of the possible identity of the phe- 

 nomena had not been perceived.* Mutations not only behave 

 like hybrids, but they may actually be hybrids, the mutative 

 variation having taken place in only one of the gamete partners 

 of the conjugation which has given rise to the variant organ- 

 ism. The partial or complete sterility of many mutations may 

 be quite the same phenomenon as the sterility of many hy- 

 brids, and may sometimes be due to the incompatibility of very 

 diverse gametes. 



Variations which come true to seed from the very first may 

 still behave as recessives when crossed, since recessive varia- 

 tions do not gain expression except when the gametes are of the 

 same kind. Other variations, though they may not come true, 

 may be dominant, or even prepotent. Thus narrow-leaved mu- 

 tations of cotton (okra-cottons) which do not come true from 

 seed may show, nevertheless, a definite and uniform prepotency 

 when crossed outside the parent type. 



The dominant and recessive relations are not, as some have 

 supposed, evidences of incompatibility or failure of the gametes 

 to accomplish normal and complete conjugation. Indeed, the 

 present perceptions enable a definite distinction to be drawn be- 

 tween terms which are not truly synonymous, though often so 

 used. Dominant and its alternative, recessive, have reference 

 to the relations of gametes as shown in the characters of con- 

 jugate organisms. The character which secures expression is 

 called dominant^ while that wlfich remains abeyant or is not 

 expressed is called recessive. 



' Cook, O. F., 1904. The Vegetative Vigor of Hybrids and Mutations. Proc. 

 Biological Society, Washington, 17 : 83 



