GABRIELLE L. C. HOWARD. 99 



this could not be confirmed by direct measurement. These 

 cultures were very luxuriant and over-grew their normal limits. 

 The question is complicated by the fact that the indentation 

 of Type 38 is sudden and short, while it is gradual in Type 23. 

 Indications of a segregation in this direction were also observed. 

 These results indicate that the apparently stalked varieties 

 of tobacco are not really petiolate, but sessile. This 

 explains the alate nature of the petiole and the fact that in many 

 such types the upper leaves are sessile, the lower petiolate. 



Further evidence on this point was obtained from the other 

 two crosses. Many cases in which the form of the lower part 

 of the leaf varied, but the indentation factors did not differ 

 so widely as in Type 23 and Tj^pe 38, were observed in the F4 

 generation of the cross Type 9 x Type 51. No petiolate forms 

 occurred, showing that the combined effect of the indentation 

 factors was not great enough to remove all the lamina. Different 

 ranges were sho^\^l by different cultures. 



Observations in the field together with a comparison of 

 Tables XXV, XXVI and XXVII, show that these indentation 

 factors are inherited quite independently of the leaf ratio and also 

 independently of the width of the leaf. Environmental in- 

 fluences would, however, by influencing the vigour of the plant, 

 affect both alike. 



Plate XXII shows three leaves selected from culture 738-81, 

 in which both wi dth andlength are the same but the amount of in- 

 dentation at the base varies. On the same Plate are shoAvn two 

 leaves of 738-19, in which the length is the same, but the width 

 and the form of the base vary. In some cultures the configuration 

 of the base was uniform, such as 694-1. Plate XIX gives a very 

 good indication of the range obtained as regards tliis character in 

 the cross Type 16 x Type 35. The F3 cultures showed very differ- 

 ent limits of variability. In one case, culture 9, there was 

 apparently only one heterozygotic factor, a separation by eye 

 gave twenty-five plants Avith a similarly broad base in 108 

 plants. 



