550 HEREDITY 
and feathers in chickens, etc. In man many characters, among 
which are insanity and susceptibility to tuberculosis, are known 
to behave according to Mendel’s law, and Eugenics, which has 
to do with applying the laws of heredity in a way to produce a 
healthier and a more efficient race of men, has its chief sup- 
port in Mendelism. 
Mendel’s discoveries have already enabled us to make some 
notable achievements in the way of improving plants and ani- 
mals. By working according to the Mendelian conception, 
many desirable varieties of the cereals, much more desirable 
Fic. 479. — Hcight of plants in the /. generation of ‘Tom Thumb Pop 
Corn (a dwarf Corn) crossed with Missouri Dent (a large Corn). The plant 
at the extreme right is similar in height to the dwarf parent, while the one at 
the extreme left is similar in height to the Missouri Dent. After Emerson and 
East. 
ornamental plants, and various kinds of better fruits have been 
developed. 
Of course in the extended investigations in Genetics since 
1900, many situations have arisen that Mendel did not meet 
Cases have arisen in which the Mendelian behavior can be 
explained better by assuming that pairs of contrasting characters 
are due to the presence and absence of certain factors and not to 
dominant and recessive factors. According to the latter hypothe- 
sis, the tallness of the tall variety of Peas is due to the presence 
of a factor for tallness, while dwarfness in the dwarf variety is 
