CHAPTER XXVI 



THE IMPROVEMENT AND BREEDING OF WHEAT 



THE amelioration or improvement of plants consists in securing and pro- 

 pagating individuals possessing in greater degree than the unimproved 

 form those characters which render them useful or attractive to man. 



Such improvement is dependent upon three factors, namely : (i) 

 variation, (2) heredity, and (3) artificial selection. 



If all plants were exactly alike no improvement would be possible ; 

 moreover, in the case of plants, such as wheat, which are propagated from 

 seeds, unless the desirable variation from the ordinary type is hereditary it 

 is useless. 



It is important to emphasise the fact that the creation of plant char- 

 acters is beyond human power, and the causes which lead to the produc- 

 tion of hereditary variations are quite unknown. 



Given, however, the improved hereditary variant, all that is necessary 

 is to select and isolate it from its neighbours and grow it. Such selection 

 is, in fact, the only means of improving plants. Selection, of course, does 

 nothing more than select, and in itself produces or creates nothing, 

 although it is frequently tacitly assumed to be causally responsible for the 

 modifications which are secured. 



The new individuals which are selected may arise spontaneously among 

 ordinary crops, or they may appear among the progeny of artificial hybrids. 



It should, however, be clearly understood that in the improvement of 

 plants hybridisation does nothing more than manufacture material upon 

 which selection can be exercised. Without selection, it leads to the pro- 

 duction of a multiplicity of forms, and consequent confusion. 



By crossing, individuals are obtained which differ from the parental 

 forms, but the differences are due only to a recombination of already 

 existing characters and not to the creation of any new character. 



In the improvement of wheat three methods of selection are practised, 

 namely : (i) mass selection, (2) selection of spontaneously occurring 

 individuals, and (3) the selection of plants with desirable characters from 

 the descendants of artificial hybrids. 



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