abstracts: heredity 153 



The uniformity of pure bred groups is an artificial result of restriction 

 of descent to single or narrow lines, not a return to an original stage of 

 purity and uniformity. Selection should be considered as a means of 

 regulating the expression of characters, not of eliminating characters 

 from transmission. Continued selection is necessary to maintain uni- 

 formity of expression in improved stocks. 



A fundamental distinction between transmission and expression is 

 recognized. ' The study of heredity, as far as it is concerned with the 

 actual variation of plants and animals, is the study of expression rela- 

 tions. Investigations of heredity instead of being directed so largely to 

 the discovery of the mechanism of transmission should seek first to 

 understand the relations that govern expression. As a step in this direc- 

 tion names are proposed for some of the more important expression rela- 

 tions. When the expression of one character depends upon or conduces 

 to the expression of another character the relation is called "symphanic." 

 When the expression of one character inhibits or interferes with the 

 expression of another the relation is called "antiphanic." When the 

 expression of one character neither favors nor interferes with the expres- 

 sion of another the relation is called "paraphanic." 



Other relations of expression are shown by the different results secured 

 in first generation hybrids. In some hybrids there is a blended or com- 

 bined (mixophanic) expression of the contrasted characters. In other 

 cases one of the parental characters is suppressed (hypophanic) , allow- 

 ing the opposed character to appear as dominant (epiphanic). When 

 both of the parental characters are suppressed, so that a more primitive 

 character appears, the result may be described as reversive or atavistic 

 expression (palimphanic) . 



Attention is given to the influence of external conditions upon expres- 

 sion, and to the relation of expression to vigor and fertility, including 

 intensification of characters in conjugate hybrids and degeneration in 

 perjugate hybrids. Coherence in the expression of characters derived 

 from the same parental stock is recognized as an obstacle to the formation 

 of Mendelian combinations of characters of different species. Inter- 

 mediate (metaphanic) expression of characters often involves sterility, 

 not only in hybrids between species, but also in case of incomplete differ- 

 entiation of specialized organs of the same plant. Thus in cotton 

 bract-like leaves and leaf-like involucral bracts are often accompanied 

 by sterility. The bulletin concludes with two summaries, one of general 

 conclusions regarding the nature of heredity, the other of applications 

 to methods of breeding. 0. F. C. 



