498 GENERAL MORPHOLOGY OF PLANTS 



then selects the most promising forms. By crossing different 

 varieties with the promising ones, or by crossing closely related 

 species the offspring is made more variable, which gives a wider 

 range to select from and makes possible, by this wider range of 

 variation, forms which are more productive and of better quality 

 and of a hardier nature. The crossing is brought about by 

 artificial pollination since the parents can be selected for definite 

 purposes, one parent possessing one desirable quality and the 

 other parent another desirable quality, with the result that these 

 two qualities can often be combined. This improved form can 

 then be crossed with another possessing another desirable quality. 

 The hybrid or " cross " is often crossed again with one of its 

 parents, which often induces greater variability and also often 

 gives greater fertility. This furnishes a greater number of varia- 

 tions to select from. 



669. Artificial pollination. The artificial pollination is ac- 

 complished in the following way. Before the flower is open 

 the stamens are removed from one parent, and if the stigma of 

 the pistil is not ready for the reception of the pollen the flowers 

 are covered with paper bags to exclude insects which might 

 introduce pollen from an undesirable parent. One must be sure 

 that the stamens are removed before they begin shedding their 

 pollen. The pollen is sometimes shed before the flower is open. 

 A little examination of a few flowers will show when the opera- 

 tion of emasculation, as the removal of the stamens is called, 

 should be performed. Some open the flower and with forceps or 

 a hook pull off the stamens, but a better method practiced by 

 some is to cut away the calyx, corolla and stamens near the 

 receptacle with a small pair of scissors. The emasculated flower 

 is then covered with a paper bag which is gathered and tied 

 closely to the branch at the neck in order to shut out insects, 

 until the stigma reaches the receptive stage, or until the pollen is 

 ready. When the pollen is ripe it is gathered in a small recep- 

 tacle. If one wishes to be very careful to have the pollen free 

 from that of other individuals or variety, as is necessary in care- 

 ful experimental work, the male flower should be covered with a 



