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 I, 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 fF’; in cotton and 
recommended the use of F,; 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 
malus, 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. 
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