^^-2] Setchell-Goodspeed'Claiiscn: Nicotiana Tabacum 461 



consideration of the various crosses. Besides the ' ' fundamental ' ' types, 

 there have been selected for crossing certain other types, possibly 

 fundamental, or in some cases derivative, which have been employed 

 for testing the inheritance of some particular character or group of 

 characters. All of these have been described in the first paper of this 

 volume. 



The taxouomic problems in N. Tahacum do not appear to differ 

 from those presented by many other species of cultivated plants. 

 Barley, maize, oats, rice, wheat, among others, exhibit a similar diver- 

 sity of forms with more or less obvious class distinctions. In these 

 as in N. Tabacum it appears to be an easy task to shuffle and recombine 

 characters indefinitely. Clearly there can be no segregation of forms 

 into distinct species on genetic grounds; the basis of speciation, if any, 

 must depend either upon convenience merely or what amounts to 

 practically the same thing, upon elevation of certain Mendelian char- 

 acter contrasts to a higher rank in classification than others. Since 

 the taxonomic problem, therefore, is not strictly a genetic one, it seems 

 best to follow general usage in this respect, referring all the poly- 

 morphic assemblage of forms to the one species N. Tabacum, and re- 

 garding the several races included thereunder as varieties of equal 

 rank. 



The varieties employed in this series of investigations are : N. 

 Tabacum var. alba, U. C. B. G. 30/06, previously described by Setchell 

 as "White" Tobacco; N. Tabacum var. angustifolia, U. C. B. G. 68/07, 

 previously described by Setchell as N. angustifolia; N. Tabacum var. 

 calycina, U. C. B. G. 110/05 ; N. Tabacum var. macrophylla, U. C. B. G. 

 22/07 ; and N. Tabacum var. virginica, U. C. B. G. 78/05, previously 

 described by Setchell as N. Tabacum "Maryland." In each instance 

 the University of California Botanical Garden (U. C. B. G.) number 

 contains in the numerator the accession number of the year given in 

 the denominator. The varieties have in the majority of cases been 

 grown in pure lines from the date of their receipt. In order to avoid 

 needlessly encumbering the text with scientific names, the varieties 

 mentioned above will be referred to by their varietal designations 

 only, and when reference is made to the whole group the species name 

 Tabacum will be used alone. 



Three series of cultures are described in the present article: the 

 angustifolia-macrophylla series, which has been derived from reciprocal 

 crosses of angustifolia and macrophylla; the calycina-virginica series, 

 derived in the same way from calycina and virginica; and the alba- 



