Richardson: Wheat Breeding 



133 



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STIGMA OF WHEAT FLOWER 



Portion of the style, highly enlarged. Numerous pollen grains have already 

 fallen on it and can be seen adhering to it; in several cases they can 

 be seen putting forth pollen tubes. These penetrate the stigma and 

 grow down into the ovary; one of them finally comes in contact with 

 the ovule, and fertilization ensues. (Fig. 16.) 



qualitative differences, but by the 

 quantitative factor — namely, the aver- 

 age yield of the progeny of each indivi- 

 dual selection. This principle gives a 

 far more satisfactory basis for work 

 than the judging of a plant by its mere 

 external characteristics, more especially 

 when the end sought is an increase in 

 prolificacy of a given variety rather than 

 an improvement in some specific quality, 

 such as milling excellence or rust resist- 

 ance. It is therefore of great practical 

 importance for those who are desirous 

 of effecting improvements in prolificacy 

 of our standard varieties of wheat. 



Of course, in attempting an improve- 

 ment in a given strain of wheat by any 

 of the methods described above, care 

 must be taken to avoid choosing those 



plants which excel their neighbors 

 through merely accidentally favorable 

 circumstances. 



Irregular distributions of manure, 

 variations in quality of the soil, and 

 irregular seeding obviously lead to 

 irregularities in the appearance of the 

 individual plants, and considerable judg- 

 ment is required on the part of the 

 operator to decide whether the out- 

 standing plants in a given crop really 

 excel on account of individual excel- 

 lencies or because they have been 

 specially and accidentally favored in 

 the struggle for existence. 



The second method of effecting spe- 

 cific improvements in plants is by means 

 of cross-breeding or hybridization. 



