510 University of California Publications in Botany [Vol.5 



for F4. In Fe 10 plants each of 15F^B.._^^,^^F^,F^F^,F, and ISF^H., 

 P3,P23P2P83Pi2 and in F, 10 plants each of leF.Hs.Pa.P.gP^Ps^PioPs 

 and I6F-H24P34P23P2P47P5P8 were grown. In both cases the parallel 

 populations were equivalent and the characters exhibited and described 

 in F4 remained constant. Plate 85, figure 2, is a good illustration of 

 the type of this family as fixed. A photograph of the original F, 

 plant, from which tlie family descended, is reproduced in plate 85, 

 figure 1. It will be noted that the derivative represents a fixation of 

 the characters of the original F2 selection, and that no important seg- 

 regation occurred in it either in F3 or in subsequent generations. 



5. DISCUSSIOX OF EESULTS OF THE ALBA-MACROPHYLLA SERIES 



Here again, as in the calycina-virginica series, no extended discus- 

 sion of results is necessary. Obviously the differences separating the 

 two varieties are of a complex nature genetically as in the two previous 

 cases. The series demonstrates the existence of another pair of allelo- 

 morphs for flower color in this group of Tahacum varieties, viz., Ww, 

 and the part played by it in the production of both red and light pink 

 flower color has been determined. The height contrast again proves 

 to be too complex for qualitative Mendelian formulation. As in the 

 previous cases, the establishment of stable recombination derivatives 

 proved to be a simple task. 



VI. GENERAL CONCLUSIONS 



We shall limit the discussion of these results to three main topics 

 upon which these investigations seem to have thrown some light: (1) 

 the origin and interrelationships of varieties of Tahacum; (2) the 

 methodology of Mendelian analysis in Tahacum; and (3) Mendelian 

 heredity in Tahacum. 



1. ORIGIN AXD INTERRELATIONSHIPS OF VARIETIES OF TABACUM 



As a result of extensive studies of a considerable assemblage of 

 Tahacum varieties. Comes (1905) came to the conclusion that the 

 species Tahacum could be subdivided into six fundamental varieties : 



a. var. fructicosa Hook. 



h. var. lancifolia (W.) Comes. 



c. var. virginica (Agdh.) Comes. 



d. var. hrasiliensis Comes. 



e. var. havanensis (Lag.) Comes. 

 /. var. macrophylla Shrank. 



