1907] On the Vienna Rules of Nomenclature 4] 
species, even when dealing with varieties which are classed under 
different subspecies. The same holds for subvarieties and forms. 
On the other hand the same name may be employed for subdivisions 
of different species, and the subdivisions of any one species may 
bear the same name as other species. 
Examples. — The following are admissible: Rosa Jundzillii var. leioclada 
and Rosa glutinosa var. leioclada; Viola tricolor var. hirta, in spite of the 
existence already of a different species named Viola hirta. The following are 
incorrect: Erysimum hieraciijoluum subsp. strictum var. longisiliquum and 
E. hieraciifolium subsp. pannonicum var. longisiliquum — a form of nomen- 
clature which allows two varieties bearing the same name in the same species. 
Recommendation. 
XVI. Botanists are recommended to use as little as possible the privilege 
granted in the second part of article 29, in order to avoid confusion and 
mistakes and also to reduce to a minimum the necessary changes of name 
when the subdivisons of species are raised to specific rank or vice versa. 
Art. 30. Forms and half-breeds among cultivated plants should 
receive fancy names, in common language, as different as possible 
from the latin names of the species or varieties. When they can be 
traced back to a species, a subspecies or a botanical variety this is 
indicated by a succession of names. 
Example: Pelargonium zonale Mrs. Pollock. 
$ 5. Names of hybrids and half-breeds (mules). 
Art. 31. Hybrids between species of the same genus, or presumably 
so, are designated by a formula and, whenever it seems useful or 
necessary, by a name. 
'The formula consists of the names or specific epithets of the two 
parents in alphabetical order and connected by the sign X. When 
the hybrid is of known experimental origin the formula may be made 
more precise by the addition of the signs, 9 c. 
'The name, which is subject to the same rules as names of species, 
is distinguished from the latter by absence of an ordinal number and 
by the sign X before the name. 
Examples: X Salir capreola = Salix aurita X caprea; Digitalis lutea 9 
X purpurea 3; Digitalis lutea (? X purpurea 9 . 
Art. 32. Intergeneric hybrids (between species of different genera) 
or presumably such, are also designated by a formula, and, when it 
seems useful or necessary, by a name. 
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