PLANT BREEDING 



505 



of another variety (that has not yet been pollenated) and the 

 stigma is then protected from further pollenation. The result- 

 ing seeds are planted, and the new generation is expected to be 

 different in some ways from each of the parents. Any desirable 

 individuals that appear in 

 this generation are kept for 

 further cultivation. This 

 principle has been applied 

 very extensively in the at- 

 tempt to find new and useful 

 variations, among animals 

 as well as among plants 

 (see Fig. 213). ^lanyofthe 

 most valuable domesticated 

 organisms have originated 

 through hybridization. 



367. Instability of fluc- 

 tuations. Plants normally 

 differ from each other, even 

 if they are grow^n from 

 seeds in the same fruit. 

 They also differ from each 

 other if they are growm 

 under identical conditions. 

 The differences which re- 

 sult from modification by 

 conditions or environment 

 are called fluctuating varia- 

 tions, or fluctuations, since 

 they flow up and down as 



conditions change to more favorable or less favorable. Now if 

 we find a few individuals in a plot that are superior to others 

 because they happen to have had somewhat better conditions — 

 moisture, soil materials, protection from parasites or disease— 

 we properly select them for the next crop seed. But will the next 

 crop be as much better than this year's as our seed plants were 



Fig. 213. 



Wheat varieties and their 

 hybrid 



At left, head of "bearded" wheat: at right, 

 head of "beardless"" wheat; in middle, head 

 of wheat resulting from a cross of the other 

 two types, grown at the Minnesota Agricul- 

 tural Experiment Station. (From Bergen and 

 Caldwell's "Practical Botany") 



