136 



The Journal of Heredity 



KEVDV I OK (KOSSLNG 



At left, a head of wlicat before treat- 

 ment. At right, same head prepared 

 for cross-pollination. (Fig. 18.) 



tion." He showed that crossing within 

 the Hmits of the species resulted in the 

 prockiction of a very vigorous offs]:)ring, 

 while self-fertilization tends to weaken 

 the ofifspring, and that flowers as a 

 general rule are constructed in such a 

 manner as to favor cross-fertiHzation. 

 In the case of wheat, however, it must 

 be remembered that the flowers are 

 normally self-fertilized, and that cross- 

 fertilization under natural conditions is 

 extremely rare. There can be no doubt 

 that in the cross-breeding of wheat 

 the immediate effect is a general marked 

 increase in the vigor of the cross. This 

 increased vigor finds its expression 

 generally in increased height, increased 

 stooling capacity and size of head in the 

 cross-bred progeny. Whether this in- 

 creased vigor is, however, a permanent 

 characteristic or a mere temporary 

 im]jrovcmcnt has not been definitely 

 estal)lishcd in the case of wheat. 



{b) Crossing ''breaks the type" and 

 induces variation. Cross-breeding is 

 one of the most powerful methods of 

 inducing variations in a given type. 

 There is no variety of wheat grown at 

 the present time but what has some 

 serious defect. It frequently happens 

 that given varieties are specially well 

 dowered with certain desirable qualities, 

 but are sadly deficient in other necessary 

 qualities. It is now possible by sys- 

 tematic cross-breeding to combine the 

 desirable qualities of two or more 

 individual types in one variety, and 

 eliminate any undesirable qualities. 

 Farrer relied almost entirely on this 

 method for the production of his new 

 varieties. Federation, the most popular 

 and prolific wheat in general cultivation 

 in Australia at the present time ; Cedar, 

 Bobs, and Comeback, wheats of the 

 highest milling excellence ; Florence and 

 Genoa, varieties which arc smut resist- 

 ant; and Biniyip, Thew, Bayah, Fir- 

 bank, Warren, Jonathan, and a host of 

 others have been produced by Farrer 

 ))>• means of cross-l)reechng. It is by 

 means of the variations induced by 

 crossing that improvement on existing 

 tyjjcs becomes possible. 



Obviously, the wider the initial differ- 

 ences l)elween the two plants the more 

 wi(k'l\- will the progeny vary. 



I 



