MENDELISM AND OTHER METHODS OF DESCENT 203 



veniently illuatrated by thinking of the characters of the two 

 parents as the ends of a graduated series or scale like that of a 

 thermometer. With reference to such a scale three forms of 

 discriminate descent may be distinguished. 



In the first form the offspring present a complete series of 

 gradations between the parental extremes. This may be called 

 scalar or intergraded inheritance. It resembles most nearly 

 the indiscriminate diversity of descent of natural species. 



In the second form of discriminate descent the progeny, and 

 especially the perjugate gametes, are adjusted to favor the 

 complete preservation of the divergent parental characters, or 

 poles of the series, but do not produce the connecting series 

 between. 



In the third form of discriminate descent the divergent char- 

 acters are not preserved by separate expressions, but are com- 

 bined into an intermediate average. 



Polar 



Scalar J Intermediate 



Polar. 



Inheritance of Intergradations {Scalar). — Scalar or inter- 

 graded inheritance is a method of descent in which the offspring 

 show a complete series of gradations between the divergent char- 

 acters of the parents. The result of such crosses is to release 

 again the normal tendency to diversity, so that the pendulum of 

 variations swings over the entire series of gradations between 

 the parental poles of the scale of inheritance. 



With reference to their expression in any single individual 

 the two parental characters may be said to be combined or 

 blended, but the existence of a complete series of gradations is 

 the characteristic which distinguishes this method of descent 

 from the combinations which result in a uniform or intermediate 



