This book is dedicated to my beloved wife in grateful recognition 

 of the major role that she has played in its creation. By virtue of 

 her impatient and energetic initiative, which demands immediate 

 translation of thought into experiment, and her unflagging enthusiasm, 

 which has always proved equal to the discouraging task of testing 

 each new alternative that experiment implacably imposes, she has 

 succeeded in the extraordinarily difficult task of constructing the 

 chromosome maps of Saccharomyces. This has graduated Sac- 

 charomyces from a promising organism for experimental breeding 

 to a full-fledged membership in the Drosophila-maize-Neurospora 

 hierarchy. 



