1922] 



Setchell-Goodspeed-Clausen : Nicotiana Tahacum 



493 



versus SSU, latifolia. Both ssLL and ssU are probably typical sessi- 

 LiFOLiA forms. Here again the heterozygote prolwibly shows an indis- 

 tinct type of intermediacy. 



Aa, SESSiLiFOLiA versiis auriculata : AA having the broad clasp- 

 ing leaf base characteristic of niacropliylla, and aa the deeply con- 

 stricted leaf bases with flaring auricles characteristic of auriculata. 

 The contrast here is really one of ssAA, sessilifolia versus ssaa, auri- 

 culata, for these factors are evidently latent when in combination with 

 SS or Ss. 



Fig. 2. Leaf base types of the angustifolia-macropliyUa series. Left to right: 



STENOPHYLLA, LATIFOLIA, SESSILIFOLIA, and AURICULATA. 



Some of the possible genotypes, their phenotypic expression, and 

 genetic behavior are included in table 7. Here only monohybrid segre- 

 gation is considered because it is doubtful, on account of the various 

 types of intermediacy shown by heterozygotes, M'hether it would be 

 possible to classify dihybrid and trihybrid populations satisfactorily. 



TABLE 7 



GENETIC BEHAVIOR OF VARIOUS LEAF TYPE GENOTYPES. 



