INTRODUCTION 295 



desired combinations through the hybridization of a low quality, rust-re- 

 sistant form with a variety very susceptible to rust but whose characters 

 are otherwise superior. Biffin found that susceptibility to yellow rust 

 (Puccinia glumarum) is dominant to rust resistance, in the cross between 

 Rivet and Red King, but that resistant forms appeared in the F 2 genera- 

 tion which bred true for resistance. This discovery marks a definite 

 forward step in the breeding of disease resistant plants. However, the 

 problems of disease resistance are complicated by the variability of the 

 parasitic organisms involved. 



Hybridization of maize was begun as early as 1878 at the Michigan 

 experiment station and was taken up from time to time at certain other 

 stations. In 1900 the U. S. Department of Agriculture began a large 

 series of experiments in crossing corn, using "all types obtainable." 

 This work has resulted in the distribution for trial of many promising 

 selections. Following the striking experiments of East and Shull in 

 crossing strains of corn that had been inbred for several generations, 

 many experiment stations began the crossing of varieties and strains for 

 increased production as well as for new combinations of characters. 



With cotton, the recent work of Balls in Egypt has furnished a basis 

 for the pedigree and hybridization method of breeding. Although cotton 

 is self-fertilized to a large degree, yet it is visited by insects during the 

 early morning hours so that there is always a certain amount of natural 

 crossing. It is very susceptible to environmental effects and its chro- 

 mosome number is large (haploid number 20). These conditions make 

 improvement by crossing a difficult matter. Cook noted the fact 

 that parent characters are sometimes intensified in the FI in cotton and 

 recommended the use of ^i hybrid seed of proved crosses as a means 

 of enhancing the quality of the lint. He also suggested a practic- 

 able and economical method of producing and utilizing such hybrid seed. 



Apple breeding by crossing varieties was begun by Knight but this 

 method has not been used extensively in Europe. In America the cross- 

 breeding of apple varieties probably was begun by Charles Arnold of 

 Ontario, Canada, about the middle of the last century. Other early 

 hybridizers who worked with varieties of the common apple, Pyrus 

 mains, were F. P. Sharp of New Brunswick, who began crossbreeding 

 in 1869 and C. G. Patten of Iowa, who commenced somewhat later, but 

 who has worked continuously with apples and pears since 1879. In 

 this connection recognition is due Peter M. Gideon and the host he 

 represents, who have produced new varieties of apples by raising seedlings 

 and selecting the best. Most of the new sorts obtained in this way are 

 of hybrid parentage. More recently important work on variety crossing 

 of apples has been done by Macoun in Canada, Hedrick in New York, 

 and Evans in Missouri. 



