1907] On the Vienna Rules of Nomenclature 35 
syllable sub before the name of a group, to form subdivisions of that 
group. In this way subfamily (subfamilia) designates a group 
between a family and a tribe, subtribe (subtribus) a group between 
a tribe and a genus, etc. The arrangement of subordinate groups 
may thus be carried, for wild plants only, to twenty-one degrees, in 
the following order: Regnum  vegetabile. Divisio. Subdivisio. 
Classis. Subclassis. Ordo. Subordo. Familia. Subfamilia. 
Tribus. Subtribus. Genus. Subgenus. Sectio. Subsectio. 
Species. Subspecies. Varietas. Subvarietas. Forma. Individuum. 
If this list of groups is insufficient it can be augmented by the inter- 
calation of supplementary groups, so long as these do not introduce 
confusion or error. 
Example: Series and Subseries are groups which can be intercalated be- 
tween subsection and species. 
Art. 13. The definition of each of these names of groups varies, 
up to a certain point, according to individual opinion and the state 
of the science, but their relative order, sanctioned by custom must 
not be altered. No classification is admissible which contains such 
alterations. 
Examples of inadmissible alterations are,— a form divided into varieties, 
a species containing genera, a genus containing families or tribes. 
Art. 14. The fertilization of one species by another, gives rise to a 
hybrid (hybrida); that of a modification or subdivision of a species 
by another modification of the same species gives rise to a half-breed 
(mistus, mule of florists). 
Recommendations. 
I. The arrangement of species in a genus or in a subdivision of a genus is 
made by means of typographie signs, letters or numerals. Hybrids are 
arranged after one of the parent species, with the sign X placed before the 
generic name. 
The arrangement of subspecies under a species is made by letters or num- 
erals; that of varieties by the series of greek letters a, B, y, etc. Groups 
below varieties and also half-breeds are indicated by letters, numerals or 
typographie signs at the author's will. 
Modifications of cultivated plants should be associated, as far as possible, 
with the species from which they are derived. 
Chapter III. On the manner of designating each group or 
association of plants. 
Section 1. General principles; priority. 
Art. 15. Each natural group of plants! can bear in science only 
1See observation to article 9. 
