826 Popular Editions of Station Bulletins of the 



occur to lessen the market value of the crop. Beyond the second 

 generation, the effect of the crossing in this experiment proved to 

 be detrimental. 



The fact that crossing parents not too closely nor 



Why does too distantly related increases the vigor, size and 



crossing productivity of the offspring is apparently well 



increase yield? established ; but only recently has any plausible 



explanation for this effect of cross-breeding been 

 given. 'Now, however, Mendel's experiments and observations on 

 heredity have given at least a workable theory to account for this 

 increase in size or vigor in the first generation of descendants 

 from parents of diverse characteristics, and the rapid disappear- 

 ance or reversal of this favorable effect in subsequent genera- 

 tions. 



Gregor Mendel worked in a very modest way and announced 

 his results in such an obscure publication that they remained 

 hidden from the scientific world for many years, but when 

 brought to light about fifteen years ago, furnished the long-de- 

 sired explanation for many of the problems of heredity. Ho 

 found that certain forms, features or characteristics of plants, — 

 since called " Mendelian characters " or " unit characters " — pass 

 unmodified from ancestor to descendant and therefore remain 

 the same however remote the inheritance. The same law applies 

 to animals, as well. These " Mendelian characters " in many 

 cases are not what we ordinarily consider characteristics, but are 

 biological factors, several of which may be combined to make up 

 what we call an animal or plant characteristic ; as number of joints 

 and length of joints, which are unit characters in a plant stem, 

 unite to make up " tallness." All the " unit characters " of both 

 parents must pass into their descendants of the first generation, 

 according to Mendel's laws, though they may not appear to do so. 

 If two characters are opposed, as horn-bearing and hornlessness in 

 two breeds of cattle that are crossed, only one can appear in the 

 immediate progeny of the cross though both are transmitted to and 

 by the individuals of this first generation. The " dominant " or 

 stronger one of the pair obscures or hides the weaker or " reces- 

 sive " character in this case ; but when two individuals of this 

 first generation are mated, or, in plants, when a self-fertilized 

 individual of this first cross produces seeds, the two unit char- 

 acters separate ; so that some individuals of the second genera- 

 tion show the dominant character only, some the recessive 

 character only and these individuals have not received nor can 



