: /. INTRODUCTION 

 * ** * 



specially created for man any more than for any other animal. 

 It is a general biological truth that everything lives unto itself, 

 not where it choses but where it can ; not upon what it likes 

 best but upon what it can get. 



It may seem to the student that an undue amount of attention 

 is given to variation and that a disproportionate amount of space is 

 devoted to that subject. In that event I have to say that variation 

 is not the antithesis of heredity but rather its constant and insep- 

 arable attendant, and that the facts of variation constitute the 

 best portion of that stock of information with which the student 

 must become possessed before he is ready to study the principles 

 involved in those generalizations upon which practical operations 

 may be safely based. 



One is painfully aware, too, of the necessity of ranging far and 

 wide for facts, and the student cannot fail to feel ofttimes that 

 the subject-matter in hand is far removed from agriculture. When 

 this is the case it is because we are forced to take what is avail- 

 able and make the most of it. Unfortunately the workers in 

 strictly agricultural fields are all too few and the reliable data 

 deplorably meager, though some original and I trust valuable 

 matter has been recently added to our stock of knowledge. 



While the same principles doubtless apply in thremmatology 

 as in evolution, yet important distinctions are to be observed. 

 First, there is every reason to suppose that even fundamental 

 laws apply to different species in different ways. For example, 

 Indian corn seems particularly sensitive to close breeding, whereas 

 wheat is almost exclusively inbred and has been so inbred for 

 unknown generations. Again, the circumstances of the case 

 often introduce into the problem certain economic considerations 

 not resting upon general evolution. For example, man cannot 

 afford the "countless ages " and " untold generations " which are 

 accorded nature for accomplishing results. In practical breeding 

 operations substantial results must follow at once and exhibit a 

 high degree of success within the period of a lifetime or they will 

 be discarded as valueless. 



Experience shows that the purposes, standards, and methods 

 of a successful breeder are seldom handed down from one man 

 to another, even to his own son. Even if that could be done, it 



