RULES OF NOMENCLATURE 51 



Section 2. The Type Method {Arl. 18, Rec. IV-VII) 



Art. 18. The application of names of taxonomic groups is determined by means of 

 nomenclatural types. A nomenclatural type is that constituent element of a group 

 to which the name of the group is permanently attached, whether as an accepted name 

 or as a synonym. The name of a group must be changed if the type of that name is 

 excluded (see Art. 66). 



Section S. Limitation of the Principle of Priority: Publication, 

 Starting-points, Conservation of Names {Art. 19-22) 



Art. 19". A name of a taxonomic group has no status under the Rules, and has no 

 claim to recognition by botanists, unless it is validly published (see Art. 37). 



Art. 20. Legitimate botanical nomenclature begins for the different groups of 

 plants at the following dates : 



{h) Myxomycetes, 1753 (Linnaeus, Species Plantarum. ed. 1).* 



Art. 21. However, to avoid disadvantageous changes in the nomenclature of 

 genera by the strict application of the Rules of Nomenclature, and especially of the 

 principle of priority in starting from the dates given in Art. 20, the Rules provide a 

 list of names which must be retained as exceptions. These names are by preference 

 those which have come into general use in the fiftj' years following their publication, 

 or which have been used in monographs and important floristic works up to the year 

 1890. 



Section 4. Nomenclature of the Taxonomic Groups According to Their 

 Categories {Art. 23-35, Rec. VII-XX) 



1. Names of Groups above the Rank of Family. 



Rec. IX. Orders are designated preferably by the name of one of their principal 

 families with the ending -ales. 



2. Names of Families and Subfamilies, Tribes, and Sub-tribes . 



Art. 23. Names of families are taken from the name or former name of one of their 

 genera and end in -aceae. 



Art. 24. Names of subfamilies {subfamiliae) are taken from the name of one of the 

 genera in the group, with the ending -oideae, similarly for tribes {tribus), with the 

 ending -eae, and for subtribes {subtrihus) with the ending -inae. 



3. Names of Genera and Subdivisions of Genera. 



Art. 25. Names of genera are substantives (or adjectives used as substantives), 

 in the singular number and written with an initial capital, which may be compared 

 with our family names. These names may be taken from any source whatever, and 

 may even be composed in an absolute!}' arbitrary manner. 



Recommendation X. Botanists who are forming generic names show judgment and 

 taste by attending to the following recommendations: 



(a) Not to make names long or difficult to pronounce. 



(b) Not to dedicate genera to persons quite unconnected with botany or at least 



with natural science, nor to persons quite unknown, 



(c) Not to take names from barbarous languages, unless those names are fre- 



quently cited in books of travel, and have an agreeable form that is readily 

 adaptable to the Latin tongue and to the tongues of civilized countries. 



* See page 48 for action on date for Schizomycetes. 



