CEREAL IMPROVEMENT HYBRIDIZATION 213 



white or gray oat kernels in black oats, side oat plants in 

 spreading oats, and white kernels in red-kerneled wheat. 



223. Correlation of characters. It has long been 

 supposed that certain pairs of characters are constantly 

 coexistent within the same plant, so that the discovery 

 of one indicates at once the presence of the other ; but it 

 is only in recent years that many such instances have 

 been demonstrated. These associated characters are 

 said to be correlated. 



The value of correlation in breeding, when once estab- 

 lished, is evident. It is of advantage in two ways : 



(1) if one character of a correlated pair is found in the 

 study of hybrid progeny, or of a variety under selection, 

 the other is known to be present, though it may be only 

 potentially. There is a gain in time, therefore, if the 

 second character is not yet visible or otherwise suspected. 



(2) Also any means of increasing a desirable character 

 will probably increase the other. For example, from 

 the weight of grain per spike one may predict the relative 

 extent of tillering in the following crop. Results of recent 

 investigations show that both variability and correlation 

 are increased, or rather more clearly exhibited, in pro- 

 portion as the environment becomes less favorable to 

 the plant ; e.g. through lack of fertility, lack of moisture, 

 or crowding of individual plants. 1 



224. Examples of correlation. Correlative characters 

 in cereals have been studied by Tschermak, Proskowetz, 



1 There is not entire unanimity of opinion as to the validity 

 of correlation. Tedin (1908, pp. 8-9, vide Newman) says, "I 

 do not believe in the existence of correlations between different 

 simple characters by which a certain character is said to indicate 

 the nature of another, but regard such as being simple manifes- 

 tations of the same unit character." Johannsen (1909) and 

 others have also expressed skepticism on the matter. 



