170 UNIVERSITY OF MISSOURI BULLETIN 



plished by MacDougal, in 1906, by injecting dilute solutions 

 of certain substances into the ovaries where seeds were ma- 

 turing. Thus for the first time in the history of biological 

 science, the formation of a new species was artificially in- 

 duced. 



Scarcely less in importance than the mutation theory 

 itself was the discovery by de Vries, in 1900, of a paper pub- 

 lished by Gregor Mendel, the Abbot of Briinn, in 1865, en- 

 titled "Experiments in Plant Hybridization." Mendel experi- 

 mented with the edible pea, Pisum sativum, and found that, 

 for example, when a tall variety was crossed with a dwarf 

 variety, all the plants of the first filial generation were tall ; no 

 dwarfs appeared. Tallness he called dominant over dwarf- 

 ness which he called recessive. If, now, the plants of the 

 'first filial generation were close bred, their progeny, the 

 second filial generation, were part tall and part dwarf. But 

 the genius of Mendel discovered more than this. He noticed 

 that there was a definite and constant numerical ratio between 

 the tall ones and the dwarfs. Three-fourths were dominant 

 or tall, and one-fourth recessive or dwarf. These dwarfs, 

 when interbred, gave in the third filial generation only 

 dwarfs ; they were pure recessives. The tall ones when inter- 

 bred proved to be unlike. One-third of them were pure 

 dominants (all tall) ; the other two-thirds were impure domi- 

 nants, giving rise (in the third filial generation) to part tall 

 ones and part dwarfs, and this again in the same numerical 

 ratio of three to one. This is a simple case of what is 

 known as Mendelism, and is often referred to as the law of 

 disjunction of hybrids. Mendel's discoveries have become 

 the foundation of all modern research into the nature of 

 heredity, but this is not the place to go further into details. 

 The subject became established upon both a mathematical and 

 an experimental basis, fruitful in results already obtained, 

 and big with promise for the future, both for pure science, 

 for eugenics, and for other lines of animal and plant breed- 



