1922] SetcheU-Goodspeed-Claiisen: Nicotiana Tahacum 491 



I,n Fo the variety of leaf shapes encountered was nothing short of 

 bewildering and series could be built up from them showing complete 

 intergradation from one type to another. Selection of phenotypes 

 from Fo, however, gave F3 populations in which the complexity of 

 segregation was usually reduced in a very definite fashion. Most of 

 the populations exhibited fewer classes than Fj, and the selection of 

 Fo phenotypes held the expression of F3 within very definite limits. 

 Thus selection of sessilifolia forms gave in F3 either all sessilitolia 

 or approximately 3 sessilifolia : 1 auriculata. In no case did such 

 selections give F3 populations with stenophylla or latifolia leaf 

 types. A summary in detail of the type of populations produced is 

 as follows. 



Stenophylla selections may segregate in a variety of ways. Thus, 

 type 1 showed approximate segregation into 3 stenophylla : 1 sessi- 

 lifolia. Type 21 bred true to the stenophylla characters. Among 

 STENOPHYLLA selections grown in 1917, population ITF.HoP^.Pg, 

 showed approximate segregation into 3 stenophylla : 1 auriculata; 

 ITFgHoPiTPgj 3 STENOPHYLLA :1 SESSILIFOLIA; ITF^HoPi^Po bred true 

 for STENOPHYLLA, and I7F3H2P17P22 gave a rather indefinite segrega- 

 tion of approximately 3 stenophylla : 1 sessilifolia. Latifolia 

 derivatives crossed with angustifoUa gave F^ stenophylla and F^ 

 approximately 3 stenophylla : 1 latifolia. 



Latifolia selections also segregate in perplexing fashion. The F^ 

 population of angustifoUa x macrophylla is typically latifolia in its 

 characters. Latifolia under certain conditions therefore is a very 

 complex hybrid expression. Recurrence of complex segregation of a 

 latifolia selection is shown in F3 of type 2. F3 of type 3 exhibited 

 a rather anomalous segregation ratio of petioled and sessile forms. 

 Type 5 apparently bred true, although there was one anomalous plant 

 in the population. Type 6 exhibited complex segregation, with an 

 indication of a ratio of 3 latifolia : 1 auriculata ; with subsequent 

 establishment of both latifolia and auriculata in constant races. 

 Type 7 bred true for a type of leaf like F^ ; and type 9 gave approxi- 

 mate segregation of 3 latifolia : 1 sessilifolia. 



Loriifolia and lanceolata derivatives are really variations of the 

 sessilifolia type. They were both produced in constant races. Their 

 genetic relation to the other forms is, however, not well established 

 by this series of investigations. Although these two are really ({uan- 

 titative variations from the strict sessilifolia type, nevertheless, cer- 

 tain of our data indicate discontinuous inheritance of these contrasts. 



