MENDEL'S LAW 539 



tall and short fathers with their sons. The sons of tall fathers 

 are on the average not so tall as their fathers, but approach the 

 average height of men in general. Likewise the sons of short 

 fathers are on the average not so short as their fathers, but 

 approach the average height that is normal for men. In other 

 words, a character that is extreme in the parents regresses 

 towards the normal in the offspring. Galton was dealing chiefly 

 with fluctuating variations, and this law is another way of saying 

 that fluctuating variations tend to fluctuate about a mode or 

 type that remains more or less constant throughout generations. 



Mendel's law. — Mendel's law is named after its discoverer, 

 Gregor Mendel, the Austrian monk and later abbot in the 

 monastery at Brunn. Mendel's law, commonly referred to as 

 Mendelism, and his demonstration of the value of the pedigree 

 culture method of studying heredity are the most important 

 contributions ever made to the study of heredity. 



Mendel {Fig. 47ff) was born in 1822 and died in 1884, thus living 

 in the same age with Francis Galton, Charles Darwin, Thomas 

 Huxley, and Alfred Wallace, other men noted for their contribu- 

 tions to biology. Mendel conducted his experiments in the mon- 

 astery garden, devoting to them whatever time his regular duties 

 permitted. He carefully studied the experiments of other stu- 

 dents of heredity and was quite famihar with their failures to 

 arrive at definite conclusions concerning the laws of heredity. 

 He attributed their failures to the way they conducted their 

 experiments, and was convinced that in order to obtain definite 

 results regarding the laws of heredity, a new way of investigating 

 the problem should be devised. He was in accord with the other 

 investigators of heredity that the best results could be obtained 

 by hybridizing, that is, by crossing plants differing strikingly in 

 characters, but he thought that the offspring must be more 

 carefully analyzed than previous investigators had done. 



Mendel's idea was to start with two plants having characters 

 strikingly different, so that there would be no difficulty in telling 

 which parent the offspring resembled. These plants should be 

 pure, that is, they should have no impure blood due to cross- 

 pollinations in any previous generations. They should be plants 

 that habitually self-fertilize. By choosing such plants as 

 parents 'there would be no difficulty in keeping their offspring 

 pure throughout the successive generations of the experiment. 



