GABRIELLE L. C. HOWARD. 71 



5. THE INSERTION OF THE LEAVES ON THE STEM. 



In N. tabacum the leaves are amplexicaul and in many cases 

 the lamina is decurrent. The length of this decurrent portion 

 varies from .5 to 7 or 8 centimetres. Forms with non-decurrent 

 leaves are also found. As this is one of the few characters in N. 

 tabacum in which total absence of the character is poss-ible, it 

 has been investigated in some detail. 



Particular attention was paid to the possibility of corre- 

 lation between this and other characters such as the length 

 of the internodes or the configuration of the base of the leaf, 

 but as far as can be ascertained there is no relation between this 

 character and any other. Table XI shows the lengths of the 

 decurrent portion of the lamina of three leaves and the 

 lengths of the three corresponding internodes in the F3 culture 

 15 from the cross Type 16 x Type 35. It will be seen that there 

 in no connection between the length of the internode and the 

 length of the decurrent lamina. Two of the plants are figured 

 on Plate XVII. Shortness of internode appears to have 

 no effect in diminishing the length of the decurrent portion. 

 Should the internode be shorter than the decurrent lamina, 

 the latter simph^ grows on into the next internode past the 

 next leaf (see Plate XVII, 35-3). At the base of the 

 plant where the leaves are very concentrated it is true that 

 this character cannot obtain its fuU expression, but there are 

 always longer internodes above on which the real length can be 

 observed. A limiting case might arise in which the number of 

 leaves being very large, the plant very short and the decurrent 

 portion very long, the latter was always stopped by the lamina 

 of the next leaf, but such cases must be exceedingly rare, and 

 none have been observed up to the present. 



It also seems possible that the configuration of the leaf base 

 might influence this character and that the lamina of a leaf 

 with large auricles or a broad base , would be rmore liable to 

 grow down the stem. This has, however, not been found to 

 be the case. No. 159-44, Plate XVII, shows a petioiate leaf 



