OLD TYPES AND NEW 157 



fortuitous and to a certain extent unscientific in that 

 no one can repeat the exact conditions of the experi- 

 ment and arrive at the same results. It depends upon 

 the chance mixing up of a large number of possibilities 

 and then in not being distracted or blinded by the 

 good while selecting the best. In the hands of a skilful 

 plant breeder with unlimited resources at his com- 

 mand it may result in much practical achievement, but 

 it does not particularly illuminate the path of other 

 breeders who wish to repeat the experiment. It is 

 after all a selection of phenotypes and, therefore, 

 forever open to error, since phenotypes do not always 

 indicate what the behavior of their constituent geno- 

 types will be in heredity. 



g. The Method of Mendel 



The method of Mendel, like the foregoing, depends 

 upon hybridization with the difference that the 

 desired combination is sought directly by definite 

 predetermined crosses, according to the expectations 

 of the Mendelian ratios, rather than through the 

 random result of fortuitous combinations. This 

 method has been rendered possible by the determina- 

 tion of Mendel's laws of dominance, and of the inde- 

 pendence and segregation of unit characters which 

 give to the experimental breeder definite expectations 

 and a method of procedure. 



If, upon hybridization, the desired character be- 

 haves like a recessive, then all that is necessary to 

 establish a pure stock exhibiting the character in 

 question, is to breed two recessives together, because 



