1 6 USE OF KEYS 



largely artificial and is used only for convenience. At this point, 

 as in some other places, one must note that in running a plant to 

 its family he has a choice, not of two, but of three sets of 

 characters (in this case indicated by the Roman numerals I, II, 

 III). Having determined the section to which a plant belongs, 

 one follows through the successively subordinated divisions of 

 that section, as indicated by the indentation of the lines upon the 

 page, until he arrives at the name of the family. A key to the 

 genera of each family will be found at its proper place in the 

 book, and likewise keys to the species when there are more than 

 three in a genus. 



It will be noted that the arrangement of the families in the 

 text does not follow the order of the key. This is because the 

 key is partly artificial, being arranged with a view to ease of use, 

 while in the body of the book families which have a natural 

 relationship are brought next to each other as far as possible. 

 This is also true of the arrangement of the genera within each 

 family, and even the species are arranged according to natural 

 relationships wherever these have been carefully worked out. 

 The nomenclature here adopted for plant names follows the rules 

 laid down by the International Botanical Congress, except in a 

 few unimportant details. 



