Application of Biological Principles to Plant Breeding 121 



Other necessary knowledge that can be obtained only 

 from experience is, which are the best flowers on the plant 

 to serve as parents of the cross and what is the proper time 

 for their pollination. For example, in the grasses the first 

 flowers that appear usually form larger, healthier seed than 

 the later blossoms. In most of the Solanaceae, the petunias, 

 browallias, etc., the exact opposite is true. The time when 

 the individual flow^er is most receptive to pollen is even more 

 narrowly limited. Both premature and delayed pollina- 

 tion is the cause of many failures and the optimum time 

 should be accurately determined. Having exercised these 

 precautions, it remains to study carefully the structure of 

 the flower in order that it may be emasculated, i.e., the 

 anthers removed before the pollen is shed, with sufficient 

 adroitness that neither the anthers shall be opened nor the 

 parts of the pistil injured. Only a few buds upon a single 

 flower spike should be operated upon if they are to be given 

 the best chance of development. If the buds are very 

 small and some pollen unavoidably reaches them, it may 

 be washed off with comparative safety with a dental syringe 

 if done immediately. It is often recommended that the 

 calyx and corolla be cut away when emasculating. This 

 should be avoided if possible and the floral envelopes left 

 as a protection to the pistil. After emasculation the buds 

 should be protected from foreign pollen until time for 

 pollination, and again after pollination at least until the 

 fruits have begun to form (Fig. 51). This protection may 

 be an ordinary paper bag when the crossing is done in the 

 field. It may be used with a plug of cotton around the 

 mouth if special precautions are found necessary. In the 

 greenhouse a square of thin celluloid rolled around the 

 flower and caught with two rubber bands, each end being 



