GENERAL RESULTS OF HYBRIDIZATION 509 



wheat on other farms, and 2 varieties yielded about 2 times as 

 much. The yield was increased on the farm mentioned both 

 by good farm management and by breeding into the varieties 

 stronger power of yielding. 



In 1902 one of the improved wheats, "Minnesota No. 169," 

 was given an extended trial in various parts of Minnesota. It 

 yielded on the average 33 bushels per acre, or 18 per cent more 

 than the ordinary varieties. This variety probably now covers 

 half a million acres, in several states, and yields at least two 

 dollars per acre more value than the varieties (mainly the "blue 

 stem," its parent) which it is rapidly displacing over an area of 

 several million acres devoted to hard spring wheat. The impor- 

 tance of every increase in production is evident when one con- 

 siders the annual value of our wheat crop, from $250,000,000 

 to $500,000,000. 



486. General results of hybridization. The relative impor- 

 tance of hybridization, and of continued selection alone as 

 means of securing valuable new varieties of cultivated plants, 

 is largely to be worked out in each class of plants. Plant 

 breeding as a science is too new to give material for answering 

 nearly all the questions that naturally arise in regard to how 

 varieties may be most rapidly improved. Hybridizing often 

 brings about great changes in the offspring, and there are 

 increased chances that some of the new forms will be more 

 valuable than any which could be discovered among the 

 foundation varieties. In the case of species perpetuated by 

 grafting, as of certain trees, and plants propagated by roots, 

 rootstocks, or tubers, as potatoes, 1 it is very easy to secure pure- 

 bred stocks. In plants grown from seed, especially if the 

 species is more or less open-pollinated, 2 there is always a most 

 important question as to how many generations must elapse 

 before the hybrid varieties can be selected " true to seed." 



1 Varieties among these are called clonal varieties (from don, meaning a 

 cutting or scion). 



2 That is, if the flowers are open to cross pollination. 



