392 SYSTEMATIC BOTANY. 



Characters. — By the term character, we mean a list of all 

 the points by which any particular variety, sjoecies, genus, sub- 

 07'der, order, sub-class, or class, is distinguished from another. 

 We have also two kinds of characters, which are called, re- 

 spectively, essential and natural. By an essential character, we 

 understand an enumeration of those points only by which any 

 division of plants may be distinguished from others of the same 

 nature ; such may be also called diagnostic characters. A 

 natural character, on the other hand, is a complete description 

 of a given species, genus, order, or class, including an account 

 of every organ from the root upwards, through the stem, leaves, 

 flowers, fruit, and seed. Such characters are necessarily of 

 great length, and are not required for general diagnosis, al- 

 though of great value when a complete history of a plant or 

 group is required. Those characters again, which refer to a 

 species, are called specific, and are taken generally from all the 

 organs of the plant, and relate chiefly to their form, surface, 

 division, colour, dimc7isio7i, and duration, or to characters of a 

 superficial nature, and without reference to internal structure. 

 The characters of a genus are called generic, and are taken from 

 the organs of reproduction. The characters of an order are 

 termed ordinal, and are derived from the general structure of the 

 plants in such groups, more especially of the organs of repro- 

 duction; while the characters of a class, as already mentioned, 

 are derived from certain important anatomical peculiarities 

 which the plants of such divisions exhibit. The essential cha- 

 racter of a genus, when indicated in Latin, is put in the 

 nominative case, while that of a species is placed in the ablative. 



Nomenclature. — The names of the classes are derived from 

 some important and peraianent characters which they possess, 

 relating either to their structure or mode of development. 

 Such names vary, however, according to the views of different 

 systematic botanists. Those more commonly used in this 

 country, and which have been accordingly adopted in this work, 

 are, Acotylcdones, Monocotyledones, and Dicotyledones, — terms 

 which, as we have already explained, are derived from the stnic- 

 ture of the embryo in the three classes respectively. Other 

 terms also in common use, are derived from the absence or pre- 

 sence of a stem, and its mode of development : such are Exogens, 

 Endogens, Acrogens, and Thallogens. The above names are 

 used especially in what are called Natural Systems of Classifi- 

 cation ; while the names of Classes in the Artificial System of 

 Linnseus, are derived chiefly from the number and other cha- 

 racters presented by the stamens. 



The names of the Orders in the Artificial System of Linnseus 

 are chiefly derived from the pistil and fruit. Those of Natural 

 Systems are usually taken from some well-known genus which 



