CHAPTER XXV 



HYBRIDISATION AND WHEAT HYBRIDS 



WHILE self- fertilisation may be considered the rule, examples of natural 

 hybrids among wheats are much more frequent than is generally assumed. 



Howard states that cross-fertilisation is common among wheats in the 

 hot dry climate of Northern India. 



Kornicke observed numerous hybrids among his cultures in Germany, 

 and Godron, Vilmorin, and others note the occurrence of cross-fertilisa- 

 tion in France. 



Nilsson-Ehle and Kajanus state that in Sweden a small amount of 

 crossing takes place at Svalof and elsewhere, and renders it difficult to 

 preserve the purity of select varieties when these are multiplied and grown 

 on a large scale. 



Shirreff records the crossing of some of his wheats, and natural hybrids 

 are found in small numbers annually at Reading both in experimental 

 pedigree cultures and in the open fields. 



Many of the " sports " discovered among wheats in all parts of the 

 world have proved to be natural hybrids or their segregates. 



A few wheats are distinctly protogynous, but in the majority the repro- 

 ductive organs ripen at the same time. 



There are considerable differences among them in regard to their 

 tendency to hybridise. While many forms are probably always self- 

 fertilised, others cross more or less readily when grown in proximity to 

 another kind, and in such instances it is found that crossing sometimes 

 takes place in one way only, the reciprocal hybrid being never obtained. 

 This is most obviously the case with the wild T. dicoccoides, but Nilsson- 

 Ehle records the natural hybridisation of Swedish Velvet Chaff (?) and 

 Pudel wheats ( $ ) when grown in mixtures with another form of T. 

 vulgare (Old Brown " Landwheat " <$ ), the reverse crosses being never 

 found. 



Since natural hybridisation occurs among widely different races and 

 varieties when grown on small plots, it may be assumed that it takes 

 place also in the field between plants of the same crop, and it is possible 



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