270 PBINCIPLUS OF PLANT CULTURE 



accomplish if we continue our trials a sufficient time. In 

 other words, we may often combine the good qualities 

 of two varieties into a single variety by securing a number 

 of cross-fecundations between the two (440), and rearing 

 plants from the seeds thus formed. 



439. Selection of subjects for crossing. — If the 

 object of crossing is simply to secure variation, as is 

 sometimes the case with wild fruits, the parents should 

 differ from each other as widely as possible, provided 

 only that they are capable of crossing freely. Crosses 

 between allied species, when this is possible, will be 

 more likely to accomplish the object sought than be- 

 tween plants of the same species. 



If the object is the improvement of present varieties, 

 the parents should be chosen with reference to the qualities 

 desired in the new variety. For example, if it is desired 

 to produce a hardy, late-keeping apple, of first quality, 

 any hardy variety that keeps well, whatever its quality, 

 may be crossed with any other hardy apple of first quality, 

 whether it keeps poorly or well, though of two apples of 

 first quality, the better keeper should be chosen. 



The plant-breeder should first have a definite idea of 

 the qualities he desires to secure in his proposed vari- 

 ety, and should then study with much care the qualities 

 of the varieties that he proposes to use as parents. The 

 two varieties that contain the largest number of the de- 

 sired qualities should be chosen. 



440. Cross-fecundation is accomplished through cross- 

 pollination of the flowers (151) ; i.e., by placing pollen 

 from the anthers of a flower of one of the varieties we 

 desire to cross upon the stigma of the other variety. 



441. Preparing the flower for crossing. — To pre- 

 vent self-pollination (151) in perfect flowering plants 



