8 BREEDING CROP PLANTS 



by one of its parents. He noted the uniformity of the first gen- 

 eration and the production of many types in the second genera- 

 tion some of which could not be told from the original parents. 

 The results were explained by the segregation of specific sub- 

 stances in the pollen and ovaries of the hybrid (Naudin, 1865). 



Wichura (1865) found reciprocal crosses gave like results and 

 therefore concluded that the pollen and the egg have exactly 

 the same share in the organism which results from fertilization. 

 He studied species crosses in willows but did not deal with the 

 individual characters of the species. 



Mendel's work, published in 1866, is now well known to 

 all students of genetics and plant breeding. This early paper 

 remained unnoticed until the rediscovery of the law in 1900 by 

 each of three investigators, DeVries, Correns, and Tschermak. 

 With the great advances made since that time rules can now be 

 given which furnish a reliable guide for plant breeding operations. 

 To quote from Pearl: 



"In the creation of new races by hybridization the plant breeder can 

 and does take Mendelian principles as a direct and immediate guide. 

 He has made Mendelism a working tool of his craft." 



THE RELATION OF CERTAIN BIOLOGIC PRINCIPLES TO PLANT 



BREEDING 1 



The art of plant breeding is closely related to those biologic 

 principles which furnish the foundation for the science of breed- 

 ing. For this reason there is a very close relation between the 

 development of theories of evolution and scientific methods of 

 breeding. 



The conception of evolution dates from the time of the Greek 

 philosophers in the eighth century. This was the speculative 

 period and evolutionary beliefs were not attained as a result of 

 experimentation. Until the sciences of botany and zoology were 

 built up it was impossible to do more than outline theories which 

 appealed to the judgment of the writer. 



The modern inductive period is of comparatively recent 

 times. Erasmus Darwin developed a theory of evolution which 

 he did not think entirely adequate. Lamarck gave us the first 

 well-rounded theory of evolution. It was based on the inherit- 

 ance of acquired characters. By continued use an organ was 



1 A bulletin by EAST (1907) and a book by SCOTT (1917) have helped 

 materially and have been freely used. 



