III. CLASSIFICATION AND DESCRIPTION OF TEE TYPES. 



1. Morphological characters. 



The Indian types of Nicotiana tahacum show a much 

 greater range in their morphological characters than do the forms 

 of Nicotiana rustica, described in a previous paper. In many 

 cases the differences in habit and in leaves are most marked. 

 On the other hand, some of the forms resemble each other very 

 closely and can only be distinguished by small difterences in the 

 leaves. It is sometimes impossible to be sure from one season's 

 crop whether the differences are sufficient to differentiate Such 

 forms into separate types. Further study has, however, generally 

 shown both that such small differences are wonderfully constant, 

 persisting from year to year (see types XLI and XLII), and also 

 that small differences in leaf shape, etc., are often combined with 

 small differences in the structure and mode of pollination of the 

 flowers (see types III and IV). Great difficulty has been experi- 

 enced in expressing in words the differences in the shape of the 

 leaves, and this has been increased by the fact that the shape 

 (generally due to a diminution in the width and size of the leaves) 

 often changes considerably from the base of the plant upwards. 

 It is hoped that the photographs will make up for any deficiency 

 in the descriptions. 



HABrr. 



The various Indian types of Nicotiana tahacum differ 

 considerably in habit. These differences are caused mainly by 

 the change in the length of the successive internodes of the plant. 

 They are accentuated by differences in the number, position and 

 size of the leaves and by the arrangement of the inflorescence. 



