CHAPTER XXVI 

 GENERAL CONSIDERATIONS AND CONCLUSIONS 



In these chapters on plant breeding the primary purpose has been to 

 present the methods by which breeders may make practical application 

 of genetic principles. The introductory historical treatment was in- 

 tentionally pragmatic in trend. It is only just however that students 

 should recognize the debt which modern agriculture owes to those pioneers 

 in biological science who laid the foundation for the science of genetics 

 through their experimental investigations of plant hybrids. Reference 

 has been made to a number of these men in earlier -chapters; we may now 

 briefly consider the general bearing of their work on the development of 

 plant-breeding methods. 



The Relation of Science to Plant Breeding. The influence of scien- 

 tific discovery on the early history of plant breeding is not marked. The 

 pioneer plant breeders, Van Mons, Thaer, Knight, Cooper, Le Couteur, 

 Shirreff and Hallet, undertook the production of new and improved 

 varieties, while the Linnaean theory of the catastrophic origin of all living 

 things was still accepted by most scientists. Even Hovey, Sutton, 

 Bull and Vilmorin completed most of their work before the publication 

 of Darwin's " Origin of Species. " Thus the beginnings of plant breeding 

 were made by florists, horticulturists and agronomists, who observed the 

 defects in commonly grown varieties and sought to improve them or to 

 find better ones. Each attacked the problem in the light of his own 

 knowledge or theories, the later ones sometimes profiting by the experi- 

 ence of their predecessors. 



However, while the early plant breeders were working along empirical 

 lines, the first efforts to obtain scientific knowledge of plant hybrids were 

 being made. The conception of sexuality in flowering plants began to be 

 formulated during the last quarter of the 17th century. It was in 1676 

 that Nehemiah Grew first expressed the idea that the anthers are sexual 

 organs (published in 1682). According to Focke, the knowledge of sexu- 

 ality in higher plants was really established by Rudolph Jacob Cammerer 

 (Camerarius), whose first experiments were made at Tubingen in 1691. 

 Three years later he published his "Epistola de sexu plantarum." Dur- 

 ing the first half of the 18th century the famous Swedish botanist, Carl 

 von Linne" (Linnaeus), also experimented with hybridization in plants, 

 and his cross between two species of salsify (Tragopogon pratensis and 



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