276 AGRICLXTURE OF MAINE. 



records and has its theoretical foundation in the genotype con- 

 cept of Johannsen. This working hypothesis involves the follow- 

 ing factors : 



(a) That the egg record of an individual hen gives no defi- 

 nite indication whatever as to what the probable laying of her 

 daughter will be. Examination of hundreds of pedigree records 

 leaves no doubt as to the truth of this fact. Individual birds 

 with high egg records are as likely as not to produce daughters 

 that make poor egg records and vice versa. From the laying 

 record of an individual hen it is quite impossible for anyone to 

 tell whether its progeny will be good layers or poor layers. 



(b) A flock of hens, no matter how "pure bred'" it may be, 

 is really not a homogeneous, unitary aggregation, but instead 

 it is made up of a varjang number of lines or strams, each of 

 which tends to breed true to a certain definite degree of egg 

 productiveness or fecundity. In other words such a flock is 

 a mixture of several component lines. The individuals in each 

 line tend to produce oft"spring true to the type of the line 

 rather than to the type of the population as a whole, excepting 

 in cases where by chance the population type and the type of 

 one or more lines happen to be the same. 



(c) When mass selection alters the population type it does 

 -s^ by a process of isolating from the mixture certain strains 

 whose own types are different from the original general popu- 

 lation type and which dift"er in the direction toward which se- 

 lection is made. The thing to be sought, then, in the practical 

 breeding of poultry for increased egg production is to discover 

 by means of pedigree analysis those individuals of the general 

 flock which possess high fecundity in inheritable form. These 

 individuals may then be isolated and propagated anrl improve- 

 ment thus brought about. 



^t>' 



Results of Nezv Plan. 



It has been shown that by the application of this new plan 

 of breeding it has been possible to isolate from the same stock 

 of birds which w-as used in the mass selection experiment, 

 pedigree lines or strains which for five generations (the time 

 covered by the experiment to date) have bred uniformly true 

 to definite degrees of egg production. In this work there have 



