June 19, 1916 Correlated Characters in Maize Breeding 437 



associated with the method or mechanism of heredity. An example of 

 this type of correlation is shown in the association of yellow petals and 

 deeply lobed leaves in Egyptian X Upland cotton hybrids. 



This classification differs from those proposed by Webber (1906) and 

 East (1908) chiefly in placing physical correlations outside the pale of 

 biological correlations. Most of those correlations classed by Webber as 

 morphological would here be considered as physical. This distinction 

 is made because it seems to the writer that the relation between length 

 and weight, for example, is inherent in the properties of matter and is not 

 a biological phenomenon. Certainly a relation of this kind would be 

 found in stones or any inanimate objects selected at random. 



Since physiological functions are always directly or indirectly induced 

 by or at least associated with environmental stimuli, Webber's environ- 

 mental and physiological correlations are here combined. That the 

 examples of physiological correlations cited by Webber are reverse or 

 negative correlations need not confuse the issue, since by simply stating 

 the relation in other terms the correlations can be made to appear as 

 positive. 



The distinction between physiological and genetic correlations may 

 not always be easy to apply, and the apparent need of it may disappear 

 entirely with a more complete knowledge of inheritance and methods 

 of growth. For the present, however, the distinction will be useful even 

 if physiological correlations are confined to pure lines or asexually 

 propagated stocks where differences in inheritance can be eliminated. 

 To ascribe the long intemodes of the main stem and branches to the 

 activity of a single determiner or gene is hardly less futile than to offer 

 the same explanation for the correlation between the length and weight 

 of inanimate objects. If the one is inherent in the properties of matter, 

 the other is inherent in the properties of plants. 



All examples of genetic correlation are exceptions to the third law of 

 Mendel, which implies that characters are redistributed in the perjugate 

 generations of a hybrid in accordance with the laws of chance. Con- 

 versely, all instances in which Mendelian ratios, other than the 3 to i 

 ratio of a monohybrid, are followed with exactness demonstrate the 

 action of this third law and the absence of correlations among the factors 

 which make up the characters. It should be kept in mind, however, that 

 multiple hybrid ratios have seldom been determined with any great degree 

 of accuracy, so that correlations, unless of a pronounced type, would 

 escape detection. 



The significant factor in genetic correlations is the grouping of the 

 characters in the ancestry and not the inherent properties of the charac- 

 ters themselves. Thus, when colored aleurone and horny endosperm 

 are found to be correlated in the progeny of a hybrid, involving colored 

 and white aleurone and homy and waxy endosperm, it does not indicate 



