INTERNATIONAL RULES FOR BOTANICAL NOMENCLATURE 3 
Article 13. The definition of each of these names of groups 
varies, up to a certain point, according to individual opinion and 
a state of the science, but their relative order, s sanctioned 
ustom, must not be altered. No classification i is admissible which 
contain such alterations 
amples of inadmissible alterations are: a form divided into 
a a species containing genera, a genus containing families 
or tri 
Article 14. The fertilization of one species by another nie 
rise to a hybrid (hybrida) ; that of a modification or subdivision of 
a species by another modification of the same species gives rise re a 
half-breed (mistus, mule of florists). 
REcoMMENDATIONS. 
. The arrangement of species in a genus, or in a Sse ena of 
a alas is made by means of typographic signs, letters, or nume- 
rals. Hybrids are arranged after one of the parent as with 
the sign x placed before the generic name. 
The can ore of subspecies under a species is made by letters 
or numerals ; hat of varieties by the series of Greek letters a, 8, y, 
&e. Groups ae varieties and also half-breeds se a agay by 
letters, numerals, or typographic signs, at the author 
Modifications of cultivated plants should be posse Ke far as 
possible, with the species from which they are derive 
III. On the wayemer of agen go each Group or Asso- 
iation of 
Section 1. ania care ; Priority. 
Article 15, Each natural group of plants* can bear in science 
only one valid designation, namely, the oldest, provided that it is 
in co. conformity w with the rules of nomenclature, and the conditions 
laid down in Articles 19 Aa 20 of Sect 
Ar The designation of a sa 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. 
Article17. No one should change a name or a combination of 
names without serious motives, based on a more profound know- 
ledge of facts, or ae the necessity of giving up a nomenclature that 
is contrary to 
Article 18. ‘The form, number, and arrangement of names 
“a a on the nature of each group, according to the following 
Section 2. Point or DEparTuRE FOR esos anraage Lim1tatIon 
or Principe oF Priort 
Article 19. Botanical nomenclature aia with the Species 
Plantarum of Linneus, ed. 1 (1753), for all groups of vascular 
* See observation to Article 9. 
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