2 Plant Genetics 



by comparison and inference they related certain forms 

 and then tried to explain why these forms had become 

 different. For example, Lamarck's explanation of the 

 changes was that they are the results of "use and dis- 

 use"; Darwin's explanation was that they are due to 

 "natural selection." 



It was in 1900 that a new method for the study of 

 evolution was announced with the appearance of The 

 mutation theory by De Vries. The new method was 

 experimentation. Instead of comparing two species 

 and inferring that one of them had produced the 

 other, species were bred through successive generations, 

 under rigid control, and were observed to produce new 

 species. The old method inferred that a certain thing 

 occurred; the new method saw it actually occurring. 



In developing this experimental method the facts 

 of inheritance began to accumulate. Presently the 

 facts accumulated sufficiently to be organized into 

 theories of inheritance, and the special field of genetics 

 was the result. In brief, therefore, genetics is the 

 experimental study of inheritance. Aside from the 

 interest of genetics itself, its possible applications are 

 even more important. For example, it will probably 

 eventually explain organic evolution; and, most impor- 

 tant of all considerations, it will probably enable us to 

 control plant and animal breeding in a way that will 

 be of the greatest practical importance in agriculture. 



It should be realized that, in so complex a subject as 

 heredity, increasing experimental work must greatly 

 increase the range of known facts and make explanations 

 increasingly difficult. The facts of inheritance obtained 

 from experimental work with a few simple forms 



