20 



TOBACCO BREEDING. 



crossing, for each flower is visited many times a day by various in- 

 sects and often by humming birds ; and, secondly, it brings about con- 

 ditions favorable for the production of seed of weak vitality. Pre- 

 vious experimenters have pointed out the fact that the best seed is not 

 produced as a result of premature or late pollination, either of which 

 is likely to occur in the case of tobacco flowers under natural con- 

 ditions. "When fertilized only by pollen of the same flower, the 

 pollination takes place at exactly the right time, or when the stamens 

 push past the receptive stigma, which results in the production of a 

 superior grade of seed. 



The readiness with which tobacco flowers can be cross-fertilized 

 greatly facilitates the opportunity for producing new and valuable 



varieties by artificial cross- 

 ing. In the course of the 

 experiments here recorded 

 it has been found per- 

 fectly possible to combine 

 certain desirable qualities 

 found in different strains 

 and at the same time to 

 eliminate some of the un- 

 desirable characters by pro- 

 ducing hybrids between 

 strains of tobacco. 



The method of cross-pol- 

 lination used in the experi- 

 ments of the writers is to 

 remove all capsules, open 

 flowers, and flower buds 

 from the flower head ex- 

 cept those which are in the 

 proper stage of develop- 

 ment to open within the following twelve or fifteen hours. In 

 preparing these remaining flowers they must be carefully opened 

 and emasculated by the use of a scalpel, small scissors, and a fine pair 

 of forceps, as illustrated in figure 4. Great care must be taken in re- 

 moving the anthers before they have dehisced, in order to avoid 

 injury to the stigma. The emasculation should be done in the after- 

 noon, after which all of the flowers must be carefully covered with a 

 thin paper bag as a protection against insects or other agencies 

 whereby pollen might be transferred to them. In the forenoon of 

 the following day the emasculated flowers should be ready for polli- 

 nation, but the exact time for apptying the pollen must be determined 

 in the case of each individual flower by the appearance of the viscid, 

 sticky fluid on the surface of the stigma. The pollen from the male 



96 



Fig. 4.— Three tobacco flowers at proper stage for emascu- 

 lation, and the scissors and forceps used in emasculat- 

 ing flowers. The corolla of the central flower has been 

 opened in order that the anthers may be conveniently 

 removed. The flower on the left has been emasculated 

 preparatory to cross-pollination. 



