EARLY IDEAS ON INBREEDING AND CROSSBREEDING 7 



happened. The inbred stock seemed to grow sterile, but vigor could be re- 

 established by outcrossing. The actual cause of degeneracy in the inbreds 

 was not understood until Mendelian inheritance was discovered, but the 

 remedial procedures of the practical breeders could hardly have been im- 

 proved on. We owe to them the basis of our finest stocks. They inbred to 

 add up and concentrate desirable qualities and then crossbred to prevent 

 degeneration, then inbred again and crossed again, all the time selecting 

 their breeding stocks most carefully. Charles Darwin (1868) described this 

 process most accurately and listed the pertinent publications. 



There was a striking divergence in this work between theory and prac- 

 tice, which is just as well, as the only theories available at the time were in- 

 adequate. Those breeders who held that inbreeding was the suninmm bonum 

 did not hesitate to crossbreed when the occasion demanded, and those who 

 emphasized the virtues of hybridization inbred whenever inbreeding gave 

 them the opportunity of adding up desirable qualities. Darwin, himself, 

 stated, "Although free crossing is a danger on the one side which everyone 

 can see, too close inbreeding is a hidden danger on the other." We await 

 the twentieth century for a real improvement in breeding methods. 



The first plant hybrid was described as such in 1716, and during the next 

 forty-five years many descriptions of hybrid plants were published. Some 

 attempts were even made to produce new varieties, but in retrospect the 

 work seems somewhat dilettante. 



From 1761 to 1766, Josef Gottlieb Koelreuter (1766) published the several 

 parts of his well-known classic, and plant hybridization was put upon a 

 different and more scientific basis. His investigation of hybridization was 

 intensive, systematic, and scientific. He described, among other things, 

 hybrid vigor in interspecific crosses in Nicotiana, Dianthus, Verbascum, 

 Mirabilis, Datura, and other genera (East and Jones, 1919). He also observed 

 floral mechanisms which insured cross pollination and assumed in conse- 

 quence that nature had designed plants to benefit from crossbreeding. It is 

 worth emphasizing that hybrid vigor in plants was first described by the 

 person who first investigated plant hybrids in detail. Koelreuter continued 

 to publish papers on plant hybrids until the early nineteenth century. 



Meanwhile other contributions had been made to our knowledge of the 

 effects of outcrossing and the mechanism for securing it. In 1793, Sprengel 

 depicted the structure of flowers in great and accurate detail, and showed 

 how self pollination was generally avoided. In 1799, Thomas Andrew Knight 

 described hybrid vigor as a normal consequence of crossing varieties and 

 developed from this his principle of anti-inbreeding. Other hybridizers 

 noted the exceptional vigor of many of their creations. Indeed, hybrid 

 vigor in plants was becoming a commonplace. Among the botanists who 

 recorded this vigor were: Mauz (1825), Sageret (1826), BerthoUet (1827), 

 Wiegmann (1828), Herbert (1837), and Lecoq (1845). Gartner (1849) was 



