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IV. THE COMPOSITION OF A RACE OF CEREALS AND ITS 

 VARIABILITY.- 



Biotypes and Elementary species 43 



Multiformity of Probstier oats 43 



Independent nature of different characters 47 



Natural crossing in cereal grains 48 



Individual and partial modifications within pure lines 49 



Influence of mass-selection 50 



THE ORIGIN OF ' ABERRANT FORMS ' AS QUANTITATIVE HEREDITARY 



VARIATIONS 50 



-Mendel's Law of Hybrids 51 



The theory of Presence and Absence 57 



The theory that certain characters may possess more than one 



unit, each of which has the same external effect 60 



Crossings between sorts which are apparently identical in regard 



to certain characters 61 



Crossings between sorts which differ in regard to certain 



characters 64 



THE ORIGIN OF ' ABERRANT FORMS ' AS ' MUTATIONS ' 70 



THE NATURE AND CLASSES OF VARIATION (SUMMARY) 72 



AN EXPLANATION OF THE OCCURRENCE OF CERTAIN ABERRANT 



FORMS UNDER DOMESTICATION 74 



Kotte (cone) wheat 74 



Reappearance of dominant heterozygotes infield cultures 74 



V. PRACTICAL APPLICATION OF PRINCIPLES NOW RECOG- 

 NIZED IN CEREAL BREEDING AT SVALOF 



Line Breeding 76 



Artificial hybridization 78 



The necessity of systematic crossing work 79 



Two categories into which crossing work at Svalof falls 81 



Repeated crossings 81 



Obtaining constancy in new combinations 81 



Creating of plant populations 82 



Mass-selection 83 



PRACTICAL IMPORTANCE OF SORT PURITY 86 



Definition of a " Sort " 86 



VI. METHODS OF WORK IN CEREAL BREEDING AT SVALOF. 



Size and arrangement of plots *7 



Pedigree cultures 87 



Head-to-the-row method 89 



Preliminary trial plots 90 



Large comparative trial plots 93 



Importance of a proper interpretation of results 95 



