8 MICROSCOPIC ANATOMY OF THE TEETH 



These short plants he called the Recessives. 



The recessives when self -fertilized gave pure short plants, 

 the short variety remaining pure in succeeding generations. 



The dominants, however, continued to yield both pure 

 tall plants and also mixed plants, showing in successive 

 generations the same proportion of three tall to one short. 



As stated by Bateson (1), ' the whole F 2 generation, there- 

 fore, formed by self-fertilization of the original hybrid, con- 

 sists of three kinds of plants : 



25 per cent. 50 per cent. 25 per cent, 



pure dominants impure dominants pure recessives 



or three dominants to one recessive.' 



It is thus seen that a permanent pure variety arises from 

 the mixed variety, and in this instance a fixed law of varia- 

 tion is established. 



Many experiments demonstrate that these laws are 

 applicable to all living organisms, both vegetable and animal. 

 As Bateson says : * The fact of segregation was the great 

 discovery which Mendel made segregation being the dis- 

 sociation of characters from each other in the course of the 

 formation of the germ.' 



Natural selection acts on variations, but how these varia- 

 tions occurred had always previously been an obscure and 

 undetermined problem. 



Mendel's researches have, to a great extent, contributed 

 to the solution of this problem, and although much yet 

 remains obscure, this discovery has given an impulse to the 

 study of heredity which cannot fail to have the most far- 

 reaching and important results. 



As the author above referred to says : ' There is nothing 

 in Mendelian discovery which runs counter to the cardinal 

 doctrine that species have arisen by means of Natural 

 Selection,' or ' the preservation of favoured races in the 

 struggle for life ', but, as he points out, the scope of natural 

 selection is closely limited by the laws of variation, and 

 Darwin would have welcomed the work of Mendel Avith 

 delight, as explaining much which he himself felt to be 

 obscure. 



