INTRODUCTION 
xi 
NOMENCLATURE 
Principles , Rules, and Reconvnendations 
In matters of nomenclature, the rules passed by the international congresses of botanists 
held at Vienna in 1905 and at Brussels in 1910 are, in general, adopted. It is necessary here 
to explain that the official report on nomenclature 1 is divided into general principles, rules, and 
recommendations. The general principles command universal assent, as the following extract will 
show : “ Art. 3. The rules of nomenclature should neither be arbitrary nor imposed by authority. 
They must be simple, and founded on considerations clear and forcible enough for everyone to 
comprehend and be disposed to accept.” 
The rules are inevitably more controversial in character than the principles ; but we have no 
hesitation in this work dn following these rules in their more important aspects. The recommen- 
dations refer to less important matters ; and, in a. few cases, we deem it desirable to depart from 
them. 
Names of the groups of plants 
The following are the groups of plants, and the names of these groups, which we, following 
the international recommendations, adopt in this work : — class (e.g., Pteridophyta ), division (e.g., 
Dicotyledones), order 2 (e.g., Salicales), family 2 (e.g., Salicaceae), tribe (e.g., Atripliceae), genus (e.g., 
Atriplex), section (e.g., Lapathum ), series (e.g., Tremulae ), species (e.g., Populus tremula ), variety (e.g., 
Populus nigra var. viridis), and forma (e.g., Polygonum amphibium forma terrestre). Intermediate 
groups are interpolated, in accordance with the international recommendations, as occasion requires : 
thus, we recognise subclass (e.g., Amentiflorae), suborder (e.g., Santalineae), subfamily (e.g., Cheno- 
podioideae ), subtribe (e.g., Loranthineae), subgenus (e.g., Obione'), subsection (e.g., Robur ), series (e.g., 
Albae ), and subvariety (e.g., Salix cinerea subvar. aquatica). We do not adopt the group “race” 
(a subdivision of a species), and only in special cases the group subspecies. 
It would, in our judgment, be a very great advantage if each of these groups had some 
definite affix by which it could invariably be recognised. Such affixes are commonly given to 
some of the groups, namely, to the order (which commonly ends with the affix -ales), suborder 
(- ineae ), family (- aceae ), subfamily (- ideae ), tribe (-eae), and subtribe (- inae ). The suggestion was 
made long ago that these affixes should be universally used for the groups in question ; and 
we think it is a pity that the suggestion has not been adopted by botanists. At present, there 
are so many exceptions to the above terminations that a beginner in botany is overwhelmed by 
them ; and he may be pardoned for regarding the botanical names of the major groups as 
chaotic. For example, the usual affix denoting an order is -ales-, but the following irregular 
names (among others) of orders are also recognised by many botanists : — Myrtiflorae, Contortae, 
Helobieae, Principes, Scitamineae, and Microspermae. Again, the usual affix denoting a family 
is -aceae ; but the following irregular names (among others) of families are also in common 
use : — Leguminosae, Guttiferae, and Compositae. In the present work, the affixes in question 
(namely, -ales for orders and -aceae for families) are regarded as absolute. The affix is always 
appended to the stem of the name of an existing genus ; and thus such names as Ranales, 
Rhoeadales, Parietales, and Caryophyllaceae will disappear. 
Starting-point of nomenclature 
Botanical nomenclature, for the vascular plants, begins with the publication of the Species 
Plantarum (2 volumes) of Linnaeus, 1753. As the genera, however, in this work, are without 
1 biter national Rules of Botaiiical Nomenclature adopted by the international botanical congresses of Vienna 1905 and 
Brussels 1910 (in French, English, and German; Jena, 1912). 
2 In some British and American works, the term “cohort” is used instead of order, and the term “natural order” 
instead of family. The terms we use, order and family, are advised by the international recommendations ; and we hope 
therefore that they will be adopted by all botanists in this country. 
