1922] Setchell-Goodspeed-Clausen : Nicotiana Tahacum 483 



4 are assembled the data from pink flowering selections from popu- 

 lations which showed segregation into red and pink. In this table the 

 populations which bred true for pink are assembled in the upper 

 portion of the table, and those which showed further segregation into 

 red and pink are assembled in the lower portion. Of the 18 selections 

 made, 7 bred true for pink (or light pink), and 10 gave segregation 

 in the succeeding generation in about the ratio of 3 pink : 1 red. The 

 total figures for the 10 populations — 187 pink : 60 red — are in very- 

 satisfactory agreement with the simple Mendelian ratio. The family 

 of type 19 behaved in an anomalous fashion, which may indicate mis- 

 classification of the Fg parent ; and the family of type 2, which showed 

 only one red plant has been included among those which bred true for 

 pink. Strictly light pink selections should have given only light pink 

 flowers in subsequent generations ; the pink ones should all have given 

 segregating populations. The evidence indicates that this result would 

 be obtained if segregation occurred for only one pair of allelomorphs. 

 The difiiculty, in part at least, appears to be the result of segregation 

 of modifying factors in the populations. These factors apparently 

 have an effect on flower color sufficient to obscure segregation into 

 pink and light pink, but not enough to obscure the segregation into 

 red and pink. The actual results indicate an approximate agreement 

 with expectation, but the breeding test clearly is necessary in order 

 to determine the actual distribution of the pink individuals into their 

 genetic classes. 



6. LATER SOWINGS OF F^ AND F3 OF THE ANGUSTIFOLIA- 

 MACROPHYLLA SERIES 



In 1916 and 1917 certain families of F2 and F3 of H, were grown 

 in order to reexamine them in the light of data previously collected 

 and to determine whether or not any more definite classifications could 

 be made than those stated in the preceding pages. The populations 

 grown are described briefly below. 



I6F2H2P0, as the population number would indicate, was a sowing 

 of seed of lOFiHoPg from the original F^ population of H.. As in 

 previous cases, the segregation as regards leaf shape was so complex 

 as to preclude definite classification. The types previously noted for 

 second generation populations were all in evidence and along with 

 them practically every sort of intermediate. The height of plants 

 and general habit likewise agreed with the description previously 

 given. 



