1922] Setchell-Goodspeed-Clausen: Nicotiana Tahacum .487 



auricles of type 10 had short naked petioles. A few were strictly of 

 type 10. The following segregation ratio was noted : 61 sessilipolia : 



27 AURICULATA. 



7. CROSSES OF DERIVATIVES WITH THE PARENTS 



In the preceding account we have pointed out that by growing 

 definite hybrid selections in the pure line through a number of gener- 

 ations it has been possible to establish a certain number of stable 

 derivatives which represent more or less obvious recombinations of 

 characters of the original parents. In a Mendelian sense, they repre- 

 sent stable reorganized germinal complexes containing hereditary ele- 

 ments that have been derived from both parents. Obviously such 

 recombinations of Mendelian units must differ in fewer units from 

 either parental type than did the parental types from each other. To 

 test some of these derivatives we have crossed them with the original 

 parents, usually with the one to which they bore the closest resem- 

 blance, in order to observe how complex a type of segregation the 

 hybrids thus obtained would exhibit as compared with that of the 

 original angustifolia-macrophylla hybrids. In so far as they have been 

 studied to date, a description of these hybrids and their progenies 

 follows : 



SESSiiiiFOhiAxmacrophylla. Fg sessilifolia of type 20 was crossed 

 with macrophylla giving H-^ = type 20$ x macrophylla(^ and H-^ = 

 reciprocal thereof. The derivative parent here very closely resembles 

 macrophylla throughout in flower color and shape, habit, leaf shape, 

 etc. ISF^Hjo and ISF^H-i, two families of 50 plants each, were equiv- 

 alent in every respect. The plants were very close indeed to macro- 

 phylla, as is also the sessilifolia parent. The only difference readily 

 observed was some variation in the amplitude of the corolla. In Hgi, 

 a plant with a larger and one with a smaller corolla were selected for 

 pure seed. In Fo, grown in 1916, one family of Hjo and two families 

 of Hgi, of 50 plants each were grown. The flower color in the F, 

 populations was throughout that of macrophylla and the leaf charac- 

 ters also were those of macrophylla. All three families were remark- 

 ably uniform, not only agreeing with one another but uniform as to 

 indivduals. They all resembled closely the macrophylla type and there 

 was no definite segregation of any kind in them. The three popula- 

 tions appeared to be replicas of macrophylla throughout except that 

 they were slightly more robust. 



