PLANT LIFE. 



S3 



field just before the flowers are opening and remove 

 all plants that are very poor, or that deviate too far 

 from the ideal, so that their pollen may not reach the 

 pistils of the remaining plants and cause their bad 



TOBACCO SEEDLINGS FROM LIGHT (31-3), MEDIUM (31-2), AND HEAVY 

 (3I-I) GRADES OF SEED. 



character to be given to the next generation. Of 

 course this is unnecessary in those plants when the flow- 

 ers are self-pollinated. 



Improvement by Artificial Cross-Pollination. By 

 seed selection only those characters can be chosen that 

 happen to appear as natural variations among the 

 plants grown. We possess the power, however, by 

 artificial cross-pollination, of combining the desirable 

 characters of different plants. Of course this method 

 is limited by the fact already mentioned that only very 

 closely related plants can be crossed successfully, but 

 it is readily applicable to different varieties of the same 

 species of plant, as for example various sorts of cot- 

 ton, wheat, corn, etc. 



Examples of Artificial Cross-Pollination. A few 

 examples will show what can be accomplished. The 

 common sweet orange is killed by cold only a few de- 



