PREFACE 



THIS book has been prepared in the hope that 

 it may meet, in some small degree, what seems 

 to be a rather definite need in biological literature. 

 During the past fifteen years there has been a great 

 movement of biological research towards the prob- 

 lems of organic evolution, and particularly towards 

 that phase of those problems which constitutes 

 the subject currently known as genetics. Ex- 

 perimental breeding has become the order of the 

 day, not alone in the laboratories of zoology and 

 botany, but in the agricultural experiment stations 

 and colleges everywhere. 



Research in a new field means the application of 

 new methods. Nowhere has this been more true 

 than in genetics. For a critical handling of many 

 genetic problems, a thorough grounding in chem- 

 istry, physics, and mathematics as well as biology 

 is really a necessity. In particular the widespread 

 use of the biometric technique in biology and 

 agriculture demands a clear understanding of cer- 

 tain fundamental mathematical principles. Un- 

 fortunately such a clear grasp of underlying 

 principles is too often plainly lacking in the bio- 



