i8 ' THE PRESIDENTIAL ADDRESS 



prefer a material modus operandi to anything so vague as the action 

 of a tendency.' 



It is not necessary for me to speak on the rediscovery of Mendel's 

 great work and all that it has meant to our Biological Sections in the 

 early decades of the present century. The recent developments, 

 following the work of Haldane, R. A. Fisher, and others, and the 

 vitally important relationship between Mendelism and Natural 

 Selection were brought before us last year in Julian Huxley's 

 illuminating address to Section D. The older belief that only 

 large variations, or mutations as they then began to be called, were 

 subject to Mendelian inheritance, and that small variations were 

 not inherited at all, disappeared when further researches proved 

 that extremely minute differences were ' heritable in the normal 

 Mendelian manner,' ^^ and, with this, the foundation of Darwinian 

 evolution became immensely strengthened. It is also right to 

 remember that Bateson, the leader of Mendelian research in this 

 country, always believed in Natural Selection, regarding it indeed 

 as self-evident and not very interesting. Also that Ray Lankester, 

 as long ago as his 1906 address at York, maintained that however 

 far Mendelism was advanced it ' would not be subversive of Mr. 

 Darwin's generalisations, but probably tend to the more ready 

 application of them to the explanation of many difficult cases of the 

 structure and distribution of organisms.' 



The relationship between the germinal foundation of Mendelian 

 and Weismannian heredity was considered in a paper by L. Doncaster 

 read before Section D at the South African meeting in 1905. He 

 then maintained that Weismann's ' hypothesis that the material 

 bearer of hereditary qualities is the chromatin of the nucleus ' of 

 the germ-cells had been confirmed by recent work on their matura- 

 tion which ' has shown that they contain a mechanism which seems 

 precisely adapted to bring about that segregation of characters which 

 forms the most fundamental part of the Mendelian theory, and 

 it seems hardly possible that the two things are unconnected.' 

 MacBride also, in his address to the same section at Newcastle in 

 191 6, spoke of the ' great epoch-making discovery of experimental 

 embryology, viz. the existence of specific organ-forming sub- 

 stances.' These fundamental discoveries bring to mind a conversa- 

 tion with Weismann when he had been finally driven to frame and 

 elaborate this hypothesis, and was so appalled by the number and 

 minuteness of the material bearers of hereditary qualities contained in 

 a single germ-cell that, as he told me, he could not believe that the 

 physicists and chemists were correct in their conclusions about the 

 size of the atom. He admitted that diverse lines of evidence led to 

 1' Report, British Association, 1931, p. 77 and references quoted. 



