460 University of California Publications in Botany [Vol.5 



persists in subsequent generations in the hybrid lines. On the con- 

 trary, it has been found, as will become evident in a study of the ex- 

 perimental material communicated herewith, that a great simplification 

 occurs in the segregation in F, and subsequent generations, and that 

 continuous segregation gives way to discontinuous just as might be 

 expected from Mendelian theory. By observing the segregation in 

 the consecutive generations of hybrid lines which have become homo- 

 zygous in most of their loci through self-fertilization, it is possible to 

 obtain some idea of the Mendelian factor pairs involved iii the char- 

 acter contrasts and of their relations to one another. It has also proved 

 possible by a few years of self-fertilization to establish stable lines 

 representing recombinations of parental characters. By investigating 

 the interrelations among such stable derivative lines, which obviously 

 should differ in fewer factors from one another and from the original 

 parental varieties than the parental varieties differ from each other, 

 it would seem possible to develop an indirect mode of attack by which 

 the Mendelian analysis could be refined to any desired extent. The 

 original plan of the investigation, therefore, having as its purpose a 

 demonstration of the possibility of securing by hybridization stable 

 derivative lines representing recombinatons of characters contained in 

 the parents and comparable to the numerous existing varieties of N. 

 Tahacum, has been diverted into a detailed study of Mendelian differ- 

 ences among a typical set of N. Tahacum varieties. 



II. PLAN OF THE WORK 



In the introductory paper the senior author has discussed the fun- 

 damental types of N. Tahacum, and as indicated there, has expressed 

 a preference for selecting some five fundamental varieties, or species, 

 as representing the basal morphological elements found, or seemingly 

 to be detected, in cultivated races of N. Tabacuni. There is no neces- 

 sity for discussing further, at present, the reasons for preferring the 

 particular types selected by us as against those of either Comes or 

 Anastasia (1906), since the fundamental conceptions agree sufficiently 

 well and the important thing has been to make a beginning in experi- 

 mentation by using varieties which present seemingly fundamentally 

 different character complexes in most characteristic form in plants 

 breeding true to type in the pure line. Certain reasons for selecting 

 a particular type or types will be discussed in connection with the 



