MORE RECENT INVESTIGATIONS OF MENDELISM 549 



heredity. First, Mendel's discoveries have impressed upon us 

 the value of pedigree cultures in investigating problems of 

 heredity. Second, they afford us laws concerning the appearance 

 of characters in the offspring, whereby we know what to expect 

 and can thereby interpret results which were previously a medley 

 and not understandable. Third, knowing how characters behave 

 in the offspring when plants or animals are crossed, we can start 

 in our crossing work with definite results to be obtained in mind, 

 and also plan a definite method of procedure to obtain the desired 

 results. Fourth, owing to the discovery of the segregation of 

 characters, we now know that, in the second generation of 

 hybrids, individuals that are perfectly pure occur in definite 

 proportions and that purity of plants and animals in respect to a 

 character does not necessarily depend upon a long series of selec- 

 tions as was formerly the notion. Fifth, the law of dominance 

 explains why plants or animals impure in respect to a character 

 may appear just as pure as pure individuals. Sixth, knowing that 

 some characters are recessive and are entirely obscured by the con- 

 trasting dominant characters, we can now explain the appearance 

 in the offspring of a character which did not appear in the parents 

 or even for generations back, and in this way account for many 

 of the variations in offspring, such as an occasional plant of 

 bearded Wheat among beardless Wheat with bearded ancestors, 

 an occasional cow giving no more milk than her wild ancestors, 

 pigeons slaty blue like the wild pigeons among buff and white 

 domestic pigeons, etc. Seventh, Mendel's discovery that char- 

 acters behave as independent units in heredity and thus may be 

 separated and combined in various ways shows how it is possible 

 to breed plants and animals so as to eliminate undesirable char- 

 acters and also how it is possibe to bring together in one individual 

 the desirable characters of two or more varieties. 



More recent Investigations of Mendelism. — Since the discov- 

 ery of Mendel's paper, numerous investigators have been apply- 

 ing and testing out Mendelism. In both plants and animals 

 numerous pairs of characters have been found to behave in ac- 

 cordance with Mendelism. In plants alone more than 100 pairs 

 of characters of various kinds have been found to behave according 

 to the Mendelian conception. Among plants, color and shape of 

 flowers; color, shape, size, and quality of fruit and seeds {Figs. 

 478 and 479); time required to mature; resistance to disease. 



