520 University of California Publications in Botany [Vol. 5 



VII. SUMMARY 



Studies of three intervarietal crosses in Tahacum demonstrate that : 



1. All the differences between varieties of Tahacum can be analyzed 

 in a Mendelian fashion, if sufficient refinement in methods be intro- 

 duced. 



2. Stable recombinations of parental characters can readily be 

 obtained with three or four generations of self-fertilization. 



3. Characters outside the range between the parents are sometimes 

 produced following hybridization, and these may be readily established 

 in stable lines by self-fertilization. 



4. The petioled leaf base of angustifolia and the sessile leaf base 

 of macrophylla differ in at least three pairs of factors. 



5. A single factor difference exists between normal and split hose- 

 in-hose flowers. 



6. Two pairs of factors account for the relation existing between 

 red, light pink, and white flower color. A third pair of factors is 

 necessary to account for dark red. 



On the theoretical side it has been pointed out that : 



1. Derivation of relationships and erection of systems of classifi- 

 cation after the manner of Comes and Anastasia cannot be relied upon 

 unless supported by experimental evidence. 



2. An adequate scheme of classification should be based upon iden- 

 tities and dissimilarities in the genotypes, irrespective of the derivation 

 of the forms in question. 



3. Mendelian analysis in Tahacum requires that special attention 

 be paid to residual portions of the genotype, so that the factor differ- 

 ences under consideration act in a stable residuum most favorable for 

 emphasis of the character differences under investigation. 



LITERATURE CITED 



Allard, H. a. 



1919. Some studies in blossom color inheritance in tobacco, with special 

 reference to A'^. sylvestris and N. Tabacum. Am. Nat., vol. 53, pp. 

 79-84. 



Anastasia, G. E. 



1906. Le varieta tipiche della Nicotiana Tabacum L. Scafati. 

 Bridges, C. B. 



1919. Specific modifiers of eosin eye color in Brosophila melanogastcr. Jour. 

 Exp. Zool., vol. 28, pp. 337-384. 



