168 THE THEOKY OF EVOLUTION 



determined habitat or such peculiarities as only 

 there present themselves, show that the influence 

 of climate, temperature, and soil constitution, affects 

 the construction and nature of organisms, and, as 

 experiment shows, can also alter the form. 



Supplementary Note. Nature of the variations. 



Darwin, as is known, accepted variations which 

 were not in any particular direction and of a minimal 

 character, among which natural selection should 

 act. More recently there have been made observa- 

 tions and experiments which show that in many 

 individuals considerable variations can suddenly 

 appear, the constitution of which can be to some 

 extent estimated beforehand. 



Thus H. de Vries l observed that with the Evening 

 Primrose (Oenothera Lamarkiana) within a short period 

 seven new species arose. Such sudden deviations 

 from the parental type, apparently without any 

 external reason and which remain constant, he 

 termed ' mutations/ 



Mendel's 3 experiments have shown that by crossing 

 two races of plants differing in one or several characters 



1 Die Mutationstheorie, I, Leipzig, 1901, p. 151. 



2 Upon the experiments of Abbe Gr. Mendel (published 1865 and 1869, 

 but then forgotten and again ' discovered ' in 1900, simultaneously by 

 Correns, de Vries and Tschermak) there is based an entire literature. 

 Mendel's work has newly appeared in Ostwald's Klassikern der exacten 

 Wissenschaften, No. 121, Leipzig, 1901. See Bateson's The Methods 

 and Scope of Genetics, Cambridge, 1908 ; and Mendel's Principles of 

 Heredity, Cambridge, 1909 ; W. Johannsen's Elemente der exacten Erblich- 

 keitslehre, Jena, 1909 ; C. Correns, Uber Vererbungs Gesetze, Berlin, 1905 ; 

 J. P. Lotsy, Vorlesungen iiber Descendenztheorien, I, Leipzig, 1906, p. 99. 



