86 INTROGRESSIVE HYBRIDIZATION 



culate an average ear from each of these samples. One can 

 then compare the averages of fields, town by town or region 

 by region. By this method it was possible to demonstrate 

 (Anderson, 1946) in an exact and objective summary, how 

 the prevailing corn type changes, within 300 miles, from the 

 wide-kerneled, few-rowed types of western Mexico to the 

 many-rowed, small pointed kernel types of central Mexico. 

 By choosing appropriate characters and symbols this method 

 can be adapted to any kind of material. On page 97, in a 

 demonstration of the method of extrapolated correlates, 

 pictorialized scatter diagrams are fitted to Riley's data on 

 introgression in Iris. 



IDEOGRAPHS 



Though these have been employed in a number of different 

 problems, they are not so generally useful in population 

 studies as scatter diagrams. They are laborious to make and 

 difficult to reproduce in quantity. However, in certain prob- 

 lems in which it is important to demonstrate all the relation- 

 ships between a number of different measurements they are 

 greatly superior. Ideographs are even more pictorial than 

 scatter diagrams. In making them the original measure- 

 ments are recombined in a diagram that is a more or less 

 conventionalized representation of the object measured. 

 They have been used extensively by Alpatov (1929) in his 

 work on geographical differences in bees and in Anderson's 

 studies of iris (1936c). In this latter work, the four measure- 

 ments (length and width of petal ; length and width of sepal) 

 were combined to produce a figure (Fig. 19) that represented 

 a conventionalized white petal lying on top of an equally 

 conventionalized black sepal. 



Though they are laborious to construct, the importance 

 of ideographs lies in the fact that they show so many things 

 at once. For the iris ideographs, each one shows fifteen 

 separate facts. That is, if the ideographs were to be replaced 

 with statistics, it would be necessary to employ fifteen sep- 



