34 



Recommendations. 



I. The arrangement of species in a genus or in a subdivision of a genus is made by means 

 of typographic 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 numerals; that of 

 varieties by the series of greek letters a, ß, y, etc. Groups below varieties and also half-breeds are 

 indicated by letters, numerals or typographic 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. 



Ibis. In the case of parasites, especially parasitic fungi, authors who do not give specific 

 value to forms characterized from a biological standpoint but scarcely or not at all from a morpho- 

 logical standpoint, should distinguish within the species special forms {forma specialis, f. sp.) charac- 

 terized by their adaptation to different hosts. 



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 one valid 

 designation, namely the oldest, provided that it is in conformity 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 for the different groups of plants 

 (recent and fossil) at the following dates i). 



a) Phanerogamae und Pteridophyta , 1753 (Linnaeus, Species Plantarum, 

 ed. 1). 



h) Muscineae, 1801 (Hedwig, Species Muscorum). 



c) Sphagnaceae and Hepaticae, 1753 (Linnaeus, Species Plantarum, ed. 1). 



d) Lichenes, 1753 (Linnaeus, Species Plantarum, ed. 1). 



é) Fungi: Uredinales, Ustilaginales and Gasteromycetes, 1801 (Persoon, Synopsis 

 methodica Fungorum). 



f) Fungi caeteri, 1821 — 32 (Fries, Systema mycologicuni). 



1) The starting points of the nomenclature of the following groups are reserved for 

 the consideration of the Congress at London, 1915. Schizomycetes (Bacteria), Schizophyceae (excl. 

 Nostocaceae), Flagellatae (incl. Dinoflagellatae), Bacillariaceae (Diatomaceae), 



