The progress of Grenetics since the rediscovery 

 of Mendel's papers 



l'y 

 W. Bateson, M. A.. F. R. S.. ( Cambridge. 



It is the object of the present Essay to give au account of the 

 progress in the Study of Heredity and Variation which has followed 

 the rediscovery of Mendel's work. So rapid has this progress been 

 that though little more than six years have since elapsed, a new 

 and well developed branch of Physiology has been created. To this 

 study we may give tlie title Genetics. Until the Mendeliau method 

 was api)lied, the most obvious and essential facts of heredity were 

 unperceived. 



Our knowledge of Mendel's work began in 1900, with the three 

 practically simultaneous publications of d e V r i e s (107), C o r r e n s (23) 

 and Tschermak (93j. Correns and Tschermak had both veri- 

 fied Mendel's conclusions in the case of Pisum sativum, the species 

 originally employed, and de Vries was able from his own obser- 

 vations to extend the Mendeliau principles to a number of other plants 

 which had formed the subject of his own researches. 



At this date it is unnecessary to repeat the details of these 

 earlier experiments. The essential fact which Mendel discovered is 

 the segregation of characters in gametogenesis. This process is now 

 known to occur in the development of the gametes of many animals 

 and plants. In segregation, features of structure or of physiological 

 constitution are treated as units by the cell-divisions in which the 

 germs are formed. Such segregating characters are, so far as we 

 know, always constituted in pairs. From this fact we speak of them 

 as allelomorphs, the members of each pair being alternative to each 

 other in the constitution of the germ-cells. 



