CHAPTER VIII 
HEREDITY AND EVOLUTION 
HEREDITY 
The fact that, in general, offspring tend to resemble their 
parents has been known from early times. The modern con- 
ception of the definite laws of heredity, however, is of com- 
paratively recent date and may be said to have begun with 
Mendel. In 1865, after eight years of investigation, Mendel 
read the results of his work before the Natural History Society 
of Briinn, and the following year published them in the transac- 
tions of that society. Unfortunately his results were neglected 
until independent investigations by three botanists led to their 
rediscovery in 1900. It was then found that Mendel had dis- 
covered fundamental laws of heredity. The type of inheritance 
described by him is now known as Mendelism. 
MENDELISM 
Color inheritance in the four-o’clock. The subject of inherit- 
ance can best be introduced by means of a few examples. If red- 
flowered four-o’clock plants are crossed with white-flowered ones, 
the offspring will have pink flowers. If, now, one of these plants 
with pink flowers is self-pollinated, or if pink-flowered plants are 
cross-pollinated, their offspring will consist of red-flowered, pink- 
flowered, and white-flowered plants in the proportion of one red, 
two pink, and one white. If, now, the red-flowered plants are 
self-fertilized, all their offspring will have red flowers, and suc- 
cessive generations will continue to have red flowers for as many 
generations as they are self-fertilized. In the same way, if the 
white-flowered plants are self-fertilized, their offspring will have 
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