Hybridization 113 



or cross-fertilization. Kolreuter, Sprengel, Knight, and 

 others had observed many, if, indeed, not all, the facts 

 obtained by Darwin ; but they had not generalized upon 

 them broadly, and did not conceive the relation to the 

 complex life of the vegetable world. Darwin's results 

 are, concisely, these : self-fertilization tends to weaken the 

 offspring (Fig. 31) ; crossing between different plants of the 



FIG. 31. Inbred corn plants, showing lessened vigor of growth. 

 (Adapted from Yearbook.) 



same variety gives a stronger and more productive offspring 

 than arises from self-fertilization ; crossing between stocks 

 of the same variety grown in different places or under 

 different conditions gives better offspring than crossing 

 between different plants grown in the same place or under 

 similar conditions ; and his researches have also shown that, 

 as a rule, flowers are so constructed as to favor cross- 

 i 



