HEREDITY 513 



simpler combinations. This is only another way of expressing 

 the conviction that before many years if the present activity 

 in statistical studies continues the laws of descent will be more 

 accurately known than any other phase of biological science. 

 While the individual will always be an uncertain article, as is 

 bound to be the case where the element of chance is involved, 

 yet this same chance, under the doctrine of probability, becomes 

 one of the best known and most dependable principles where 

 sufficiently large numbers are concerned. Because of this, the 

 uncertainty as to individuals gives way to the most definite 

 knowledge as to populations, all of which leads to the inevitable 

 conclusion that the systematic study of groups of individuals is 

 the only reliable way to study heredity, and the only method 

 likely to afford data from which we may safely draw conclusions 

 as to laws of descent. 



SECTION XIII MENDEL'S LAW OF HYBRIDS 



Mendel's law, as it is called from its original discoverer, 1 

 arises naturally from the principle outlined in the last section, 

 namely, that characters tend to combine in definite proportions, 

 so that the natural offspring resulting from the mating of two 

 lines of parents with different characters, B and R, is of the 

 general form B* + 2 BR + R*. Mendel's law has special refer- 

 ence to the apparently crossed portion of the population (BR) y 



1 Gregor Johann Mendel, an Austrian monk, and abbot of Briinn, was born 

 in 1822 and died in 1884. He carried out his breeding experiments mostly 

 with peas in the garden of his cloister, publishing the results in the form of a 

 few brief papers in an obscure journal in Briinn, 1853-1865. Partly from the 

 obscurity of the journal, but more from the fact that scientists were interested in 

 totally different lines of study, these papers were practically lost to the scientific 

 world for more than thirty years. Upon the appearance of De Vries' paper announc- 

 ing the rediscovery and confirmation of Mendel's law and its extension to a great 

 number of cases, two other observers came forward almost simultaneously, and 

 independently described series of experiments fully confirming Mendel's work. 

 Of these papers the first is that of Correns (1900), who repeated Mendel's 

 original experiments with peas having seed of different colors. The second is a 

 long and very valuable memoir of Tschermak, which gives an account of elaborate 

 researches into the results of crossing a number of varieties of Pisum sativum 

 (see Mendel's Principles of Heredity, by Bateson, p. 14). The latter experimenter 

 worked mostly on peas ; Correns, on peas and corn (maize) ; while De Vries 

 worked with many species and a great variety of characters. 



