INHERITANCE 283 



About thirty-five years ago, just at the opening of the modern 

 concentrated attack on genetic problems, an association of British 

 millers awoke to the fact that some active means must be taken 

 to offset the increasingly great deficiency in quantity and quality 

 of the wheat yield. Accordingly they commissioned a specially 

 trained biologist to investigate the matter. He collected many 

 different varieties of domestic and foreign Wheat, each known to 

 have one or more good qualities, and studied how these were in- 

 herited. Making use of the data thus secured, in the course of a 

 few years he produced a wheat which combined the good qualities 

 of several varieties; including high content of gluten, beardless- 

 ness, immunity to Rust, and large yield, and this 'made to order' 

 wheat proved successful in the British Isles. But with the open- 

 ing up of new territory in western Canada another obstacle was 

 encountered: the growing season was too short for the finest vari- 

 eties of wheat. This condition was quickly met by transferring 

 the quality of early ripening from an inferior grade of wheat to 

 a wheat possessing several other valuable characters. 



In a similar fashion, a host of workers have performed the im- 

 possible of a few years ago. Corn of desirable percentage content 

 of starch or sugar; cotton with long fibers of foreign varieties and 

 quick maturing qualities to escape insect ravages; Sheep com- 

 bining choice mutton qualities of one breed with the fine wool of 

 another and the hornlessness of a third; and so on almost without 

 end. Furthermore, there is no limit in sight to the new stable 

 races of plants and animals which are forthcoming as the principles 

 already known are applied, and subsidiary ones are discovered. 

 And last but not least, Man has begun to study himself as a 

 product of heredity and the process of evolution — - to determine 

 the distribution of characters in the family, and the consequences 

 of their combinations in the physical and mental make-up of the 

 individual. 



A. Heritability of Variations 



What then are the basic principles of heredity which are to-day 

 at the command of the scientific breeder? To answer this question 

 it is necessary to go into some details because no real appreciation 

 of the underlying principles involved is otherwise forthcoming. 

 Most of these details have been acquired through patient inves- 

 tigations made from the standpoint of so-called pure science — one 



