LINKAGE, CROSSING-OVER, AND THE GERM PLASM 429 



animal and the plant kingdom. In all probability it is a universal 

 phenomenon, and if so, takes place in man. There are, in fact, strong 

 indications in man that fair hair and blue eyes are linked, but they 

 show also considerable crossing-over. Similarly, red hair and a certain 

 type of disposition are popularly supposed to be linked, but crossing- 

 over may be a saving grace in this as in other cases. 



With this chapter we have arrived at the climax of discovery in 

 the field of the mechanism of heredity. This is undoubtedly the most 

 intricate consideration dealt with in this volume. In its very nature 

 it is relatively difficult to understand. We have tried to explain 

 everything in a decidedly circumstantial way, and it is hoped that some 

 success in an endeavor to attain clearness has been attained. 



