458 University of California Publications in Botany [Vol. 5 



PAGE 



VI. General Conclusions 510 



1. Origin and interrelationships of varieties of Tabacum 510 



2. Methodology of Mendelian analysis in Tabacum 513 



3. Mendelian heredity in Tabacum 516 



VII. Summary 520 



Literature cited 520 



Explanation of plates 522 



I. INTRODUCTORY 



The inception of the work on the various species of Nicotiana 

 grown and bred in the University of California Botanical Garden 

 has already been sketched in a previous number of this series (cf. 

 Setchell, 1912). As stated there, the original intention was to assemble 

 a collection of tobacco plants simply as a portion of the outfit of the 

 Botanical Garden for general instruction and display. So great was 

 the variety and evident misapplication of the names under which the 

 seeds were received, however, that it seemed advisable to attempt to 

 determine, as definitely as possible, the status of each plant. 



In this connection, the work of Comes, in particular, came under 

 consideration and especially his views as to the origin and interrela- 

 tionships of the various cultivated forms belonging to the Tabacum 

 group. Comes (1899, p. 4 and elsewhere) regards the numerous culti- 

 vated forms of tobacco as having originated in various ways from 

 certain fundamental varieties. He estimated that there are six of 

 these fundamental varieties of Tahacum, and he supposed the large 

 number of various and seemingly more or less intergrading forms to 

 have arisen through the influence of the forces of acclimatization, 

 adaptation, hybridization, and selection. Of these, undoubtedly, the 

 greater variations have been produced and perpetuated, according to 

 the ideas of Comes, through hybridization and selection. In his mono- 

 graph (1899) and in his later more exhaustive treatise (1905), Comes 

 has attempted to estimate just which of his six fundamental varieties 

 of Tahacum have cooperated in producing each one of the cultivated 

 "races" so far as known to him. 



The statements of Comes as regards the constitution of his various 

 races seem to have been based on the results of morphological study 

 rather than upon breeding analysis. The advisability occurred to the 

 senior author of attempting to test Comes' hypothesis by selecting 

 varieties seemingly fundamental in type, and through hybridization 



