IMPROVEMENT AND BREEDING OF WHEAT 411 



obtaining if bushels on 698 square feet (108 bushels per acre) of un- 

 manured land, from pedigree Nursery Red wheat seed sown singly in 

 rows 9 inches apart each way. Further, there was in his lifetime a wide- 

 spread belief in the superior quality of his pedigree seed. 



In recent times there has been much scepticism regarding the possi- 

 bility of obtaining modifications of particular characters by repeated or 

 " pedigree " selection applied to the progeny of a single self- fertilised 

 plant such as wheat. 



The doubt has arisen in consequence of the experimental results of 

 Johannsen, who failed to secure any significant alteration in the average 

 size of Dwarf beans (Phaseolus vulgaris) by selecting either the largest or 

 the smallest seeds in successive generations of self-fertilised descendants 

 which originally sprang from a single individual bean. 



To the progeny of a single homozygous organism propagated by self- 

 fertilisation, Johannsen applied the term pure line, and his evidence and 

 that of others has led to the conclusion that selection within such a line 

 has no effect. 



All that can be legitimately concluded, however, from these experi- 

 ments is that variations of the fluctuating type (p. 346) are not inherited ; 

 but to assume that so-called pure lines are incapable of heritable variation 

 is unwarranted, for hereditary sports or mutations, though somewhat 

 rare, do occur among the descendants of wheats raised from single ears. 



Commencing with a single ear of average length, repeated " pedigree " 

 selection will lead with certainty to the production of a line with an 

 increased average length if hereditary sports with longer ears arise during 

 the time selection is continued. 



Since mutations are erratic, often small, and comparatively rare, the 

 time taken to obtain improvements by selecting within lines descended 

 from single individuals will necessarily be subject to much variation. 

 Nevertheless, in spite of the irregularity of the results, the method should 

 not be discontinued or cast aside as useless. 



Selection of Hybrids and their Descendants. The observed variability 

 of hybrids and their offspring soon led to the employment of hybridisation 

 as a means of producing desirable varieties from which improved forms 

 could be obtained by selection. In the formula of the plant-breeders of 

 last century, crossing of stable varieties was practised in order to " break 

 the types " or induce them to sport, after which the fixation of desired 

 forms by repeated selection was undertaken. 



All the early wheat hybrids were produced with this object. Among 

 the most prominent and successful breeders who adopted this method 

 of wheat improvement were Shirreff in this country, Vilmorin in France, 

 Rimpau in Germany, Pringle and Blount in the United States, and 

 Saunders in Canada. 



