INVESTIGATIONS SINCE MENDEL 547 
lication and sixteen years after Mendel’s death. In 1900 his 
paper was discovered simultaneously by three students of 
genetics, Correns, De Vries, and Tschermak, who recognized 
its importance. Since that time Mendel’s law has formed the 
basis of all work in genetics. 
The Value of Mendel’s Discoveries. — Mendel’s discoveries 
have completely revised our methods of investigating and ideas 
concerning heredity. First, Mendel’s discoveries have im- 
pressed 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 depend 
upon a long series of selections 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. Sizth, knowing that some characters are 
recessive and are entirely obscured by the contrasting domi- 
nant 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 talented offspring of medi- 
ocre parents, blue-eyed children of brown-eyed parents, bad 
sons of pious preachers, rust-resistant plants of plants suscep- 
tible to rust, and so on. Seventh, Mendel’s discovery that pairs 
of contrasting characters behave independently of each other 
but may be combined in various ways makes it possible for us to 
improve plants and animals by breeding them in such a way as 
to bring the desirable characters of different varieties together 
in one individual. 
Investigations since Mendel. — Since the discovery of Men- 
del’s paper, numerous investigators have been applying and 
