Plant Breeding. 275 



variation by gathering seeds from such wild plants that 

 have been placed under high cultivation than from those 

 that have not been submitted to culture. 



b — By grotving seedlings. In plants habitually prop- 

 agated by division (345), such as the apple, potato, 

 dahlia, etc., we secure variation by growing plants from 

 seed. The parent plant, not having been fixed by long 

 selection, as is the case with varieties grown from seed, is 

 in a state of variation, and hence its progeny usually 

 vary widely. From these variable seedlings, desirable 

 individuals may be selected for fixing. Since most of 

 our varieties that are propagated by division are highly 

 developed, their seedlings are usually, though not nec- 

 essarily, inferior to the parents. 



c — By crossing varieties or species. This is the most 

 important method of plant improvement. By procur- 

 ing fecundation of the germ cell of a plant of one vari- 

 ety with pollen from a plant of a different variety or 

 species (149) through cross-pollination (151), we ob- 

 tain a variable progeny of which the individual plants 

 may be expected to resemble both parents in different 

 degrees. For example, if we secure fecundation of a 

 number of ovules of the Worden grape with pollen 

 from the Delaware grape, and plant the seeds from the 

 fruits thus secured, we may expect that some of the 

 seedlings will resemble both parents about equally, that 

 others will chiefly resemble the Worden, but will show 

 a few characteristics of the Delaware, while others 

 again will chiefly resemble the Delaware, but will pos- 

 sess a few characteristics of the Worden. It would not 

 be surprising if we secure a vine having the vigor, 



