THE ASSOCIATION OF CHARACTERS 255 



in practice or on the basis of our general conceptions of 

 association of characters. 



B. CORRELATIONS IN AGRICULTURAL BREEDING 



It seems hardly necessary to repeat the evidence given 

 in the former chapter. We may at once go into the details 

 and consider those cases, in which the correlations give 

 direct indications of valuable qualities to the agricultural 

 breeder. Of course the application of the principle of 

 correlation to the practice of selection means the judging of 

 the worth of single plants on the ground of seemingly in- 

 significant marks. 



As a first instance I choose the peas, which have been 

 studied from this point of view by Tcdin. Peas, as they 

 are commonly cultivated, are considered as belonging to 

 two nearly alhed botanical species, Pisum arvense and 

 Pisum sativum. In reality they consist of numerous ele- 

 mentary species, which are quite distinct from one another. 

 More than a hundred types may be distinguished by the 

 color of the flowers and of the seeds, by the number of the 

 kernels in the pod, by the disposition of the flowers along 

 the axis, whether solitary or placed in pairs, by the character 

 of the ramification of the stem, and by numerous other sub- 

 ordinate marks. Each of these qualities proves to be con- 

 stant in pure cultures, and each is correlated to some feature 

 which may be of influence on the harvest. Among them the 

 time of the beginning of the flowering period is related to the 

 period of the ripening of the seeds in so simple a way, that 

 it may easily be understood, and that we only wonder how 

 it has been possible that it has not previously been discovered. 

 Some individual plants produce their first flower in the axil 

 of one of the lower leaves of the stem, but others are bare of 

 flowers over a notable length. Now it would seem that this 

 was only a case of fluctuating variability, the length of time 



