36 Rhodora [Marcu 
one valid designation, namely the oldest, provided that it is in con- 
formity with the rules of Nomenclature and the conditions laid down 
in articles 19 and 20 of section 2. 
Art. 16. The designation of a group by one or several names is 
not for the purpose of describing the characters or the history of the 
group, but that we may be understood when we wish to speak of it. 
Art. 17. No one should change a name or a combination of names 
without serious motives, based on a more profound knowledge of 
facts, or on the necessity of giving up a nomenclature that is contrary 
to rules. 
Art. 18. The form, number and arrangement of names depend 
on the nature of each group, according to the following rules. 
Section 2, Point of departure for nomenclature; limitation of 
principle of priority. 
Art. 19. Botanical nomenclature begins with the Species Plan- 
tarum of Linnaeus, ed. 1. (1753) for all groups of vascular plants. 
It is agreed to associate genera, the names of which appear in this. 
work, with the descriptions given of them in the Genera Plantarum 
ed. 5. (1754). 
Art. 20. However, to avoid disadvantageous changes in the nomen- 
clature of genera by the strict application of the rules of Nomenclature, 
and especially of the principle of priority in starting from 1753, the 
rules provide a list of names which must be retained in all cases. 
These names are by preference those which have come into general 
use in the fifty years following their publication, or which have been 
used in monographs and important floristic (floristiques) works up to 
the year 1890. The list of these names forms an appendix to the 
rules of Nomenclature. 
Section 3. Nomenclature of the different kinds of groups. 
$ 1. Names of groups above the jamily. 
Recommendations. The following suggestions as to the nomenclature 
of groups of higher rank than the family will tend to clearness and uniformity. 
: ames of divisions and subdivisions, of classes and subclasses are 
taken from one of their characters. They are expressed by words of greek 
or latin origin, some similarity of form and termination being given to those 
that designate groups of the same nature. 
Examples: Angiospermae, Gymnospermae; Monocotyledoneae, Dicotyle- 
doneae; Pteridophyta; Coniferae. Among Cryptogams old family names 
such as Fungi, Lichenes, Algae, may be used for names of groups above the 
rank of family. 
