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 pioncers 
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 lght 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 Tiibingen 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 Linné (Linnaeus), also experimented with hybridization in plants, 
and his cross between two species of salsify (T’ragopogon pratensis and 
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