Darwinism and Experimentation in Botany 



125 



origination of species, except as an easy generalization; species 

 themselves are so diverse in their composition and aspect, among 

 plants especially, that it might be said with justification that 

 there are almost as many kinds of species as there are numbers 

 of genera. Evolution concerns variations, accretions, diminu- 

 tions, appearances or disappearances of qualities, and it is to 

 these manifestations that our attention is now primarily directed, 

 in the hope of advancing what has now become an exact science. 



The conception of unit characters, of which ample practical 

 illustrations are known, may be easily misapprehended. While 

 simplicity may be understood for its constitution or organiza- 

 tion, yet it is not to bt taken for granted that all of the reactions 

 of a unit character are so. On the contrary, its integrations and 

 diverse constructive values may be extremelv complicated. 

 This is well illustrated by the results of bringing two streams 

 of heredity together by inter-crossing with resultant alternate, 

 Mendelian, mosaic or fused inheritance, in which the details of 

 dominance, potency, recessivity, mutative, or correlative 

 variations may be traced. 



Having the unit character as a workable idea, and with the 

 power to manipulate examples of it in hybrids in which alternate 

 inheritance may occur, it is obvious that widened opportunities 

 are afforded for studies in the mechanism of heredity, especially 

 in the fortunate instances in which the two components of a 

 hybrid are characterized by the number, form, size or behavior 

 of the chromosomes. Some light is also being thrown upon the 

 problem of the physical basis of inheritance. 



In the last analyses all organisms are the final result of 

 the reaction or adjustment of living or self -generating matter to 

 environment, mechanical or organic. A full century lies behind 

 us since the first proposal of Lamarck as to the inertia of effects 

 of environment upon the bodies of. plants and animals, and his 

 theory of acquired characters confronts us, neither unproven 

 nor impossible. That the germ plasm may be acted upon in 

 various ways to produce alterations in the characters it trans- 

 mits from generation to generation is established. Such altera- 

 tions are not fitting or adaptive, and if fitting or adaptive changes 

 of the body itself are transmitted, we do not know it by exper- 

 ience, although the possibilities have not been exhausted. 



