406 CHARACTERS.—NOMENCLATURE OF SPECIES. 
all the points by which any particular variety, species, swbh-genus, 
genus, sub-tribe, tribe, sub-order, order, sub-class, or class, &c., is 
distinguished fromanother. We have also two kinds of characters, 
which are called respectively essential and natural. By an essen- 
tial 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 com- 
plete description of a given species, genus, order, class, &c., 
including an account of every organ from the root upwards, 
through the stem, leaves, flowers, fruit, and seed. Such cha- 
racters are necessarily of great length, and are not required for 
general diagnosis, although of great value when a complete 
history of a plant or group isrequired. Those characters, again, 
which refer to a species are called specific, and are taken gene- 
rally from all the organs and parts of the plant, and relate 
chiefly to their form, shape, surface, division, colowr, dimension, 
and duration ; or, in other words, to characters of a superficial 
nature, and without reference to their 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 reproduction. 
While the characters of a class, &c., as already mentioned, are 
derived from certain important structural peculiarities which 
the plants of such divisions exhibit. The essential character of 
a genus, when indicated in Latin, is put in the nominative case, 
while that of a species is placed in the ablative. 
2. NoMENCLATURE.—It is the object of nomenclature to lay 
down rules for naming the various kinds of plants and the dif- 
ferent groups into which they are arranged in our systems of 
classification ; in the same manner as it is the object of termi- 
nology to find names for the different organs of plants, and the 
modifications which those organs present. 
a. Species.—The names of the species are variously derived. 
Thus the species of the genus Viola, as shown by Gray in the 
following paragraphs, exhibit the origin of many such names. 
‘Specific names sometimes distinguish the country which a 
plant inhabits: for example, Viola canadensis, the Canadian 
Violet ; or the station where it naturally grows, as Viola 
palustris, which is found in swamps, and Viola arvensis, in 
fields ; or they express some obvious character of the species, 
as Viola rostrata, where the corolla bears a remarkably long 
spur, Viola tricolor, which has tri-coloured flowers, Viola ro- 
tundifolia, with rounded leaves, Viola lanceolata, with lanceolate 
leaves, Viola pedata, with pedately-parted leaves, Viola primu- 
lefolia, where the leaves are compared to those of a Primrose, 
Viola asarifolia, where they are likened to those of Asarwm, 
Viola pubescens, which is hairy throughout, &c. Frequently 
