1922] Setchell-Goodspeed-Clausen: Nicotiana Tahacum 511 



Inasmuch as practically every Tahacum variety shows combinations 

 of characters of two or more of these fundamental varieties, Comes 

 assumed them to have been derived mostly through hybridization be- 

 tween the fundamental varieties, and he proceeded from purely morph- 

 ological studies to classify the different commercial varieties on the 

 basis of their supposed hybrid derivation. Anastasia (1906), who 

 has criticized this scheme of Comes very severely, reduced the number 

 of fundamental varieties to four, striking out fructicosa and lancifolia 

 from Comes' list, and substituting purpurea for macrophylla. Al- 

 though disagreeing as to the fundamental varieties, Comes and Ana- 

 stasia seem to agree in referring existing varieties to derivation, mostly 

 through hybridization, from a relatively small number of fundamental 

 varieties. 



The Howards (1912) object to the mode of classification of Comes 

 and Anastasia, and point out as a result of their studies of types of 

 Indian tobaccos that no attempt at classification based on derivation 

 can be considered seriously unless supported by actual experimental 

 studies. In her later paper in particular Miss Howard (1913) shows 

 that segregation products may be obtained through hybridization 

 which transcend the limits set by the parents. The Howards propose 

 a scheme of classification based primarily upon leaf and habit char- 

 acters, and they adopted this morphological system purely as a pro- 

 visional means for facilitating identification and reference among the 

 numerous forms of Indian tobaccos. 



Our results agree with those stated by the Howards, and we raise 

 the same objection to schemes of classification such as Comes and 

 Anastasia have advocated. Any scheme of classification based on 

 morphological considerations alone cannot well meet with the approval 

 of geneticists, for it does not take into account genotypic differences 

 which exist among forms of similar morphological appearance. Thus 

 it is possible, as Miss Howard points out, by crossing different mem- 

 bers of a given group to obtain segregation products which belong in 

 an entirely different morphological group in the scheme of classifica- 

 tion. In particular she points out that "petiolate" forms have been 

 produced as segregation products from two "sessile" parents, yet 

 "petiolate" and "sessile" have been used as primary indexes for 

 classification of tobaccos into groups. 



The difficulty from the genetic point of view with any classification 

 of Tahacum varieties is the same as that which is met with in tlie 

 classification of varieties of other polymorphic species. Taking the 

 species as a whole and viewing the entire assemblage of its varieties, 



