GABRIELLE L. C. HOWARD. 105 



often from the parents — the range of variation diminishing 

 with further selection. Certain cultures showed so small a 

 range of variation as to appear uniform ; some of these 

 resembled the parent forms, some were new. 



6. Observations on the time of flowering during four 

 generations resulted in the isolation of a culture flowering slightly 

 earlier than one parent, and others flowering much later, together 

 with some in which the range of variation was great. 



7. It has been shown that although the heights of tobacco 

 plants may only differ slightly, nevertheless the factors on 

 which such heights depend may be almost all different. In one 

 cross, a new form (probably uniform) much shorter than the 

 shorter parent, has been isolated ; in another cross, forms 

 resembling both parents were obtained. If there is a basal 

 conditionof height common to all tobacco plants it must be small. 



8. The number of leaves per plant does not depend on the 

 height of the plant and is practically independent of the environ- 

 ment. The inheritance of this character can be explained by 

 a basal condition (of not more than nineteen leaves) common to 

 all types of N. tahacum, combined with independent factors 

 which can add to this number. These factors are probably 

 different in magnitude, that is, they represent an addition of 

 different numbers of leaves. 



9. Distinct segregation has been observed as regards the 

 arrangement of the leaves on the stem. The arrangement wdth 

 internodes of equal length invariably breeds true. 



10. The length of the decurrent portion of the lamina is 

 probably due to the existence of several factors. Hybridization 

 between plants whose leaves are equally decurrent has produced 

 forms with nondecurrent leaves. The differences in length due 

 to the various factors may be very small. 



11. The most suitable leaves for measurements of the 

 lamina are those in the centre of the plant. 



12. The venation of the leaves is one of the most constant 

 characters of the plant. On hybridization, the parent forms 



