XX 
INTRODUCTION 
With regard to the distribution of plants in foreign countries we have relied largely on the 
following sources of information : — 
Index Kewensis (1893 — 1895), by B. Daydon Jackson. 
Supplements to Index Kewensis, by Durand and B. Daydon Jackson, Thistleton-Dyer, and Brain. 
Genera Siphonogamarum (1900 — 1907), by de Dalla Torre and Harms. 
Plantae Europaeae (1890 — ) i, ii (part), by Richter and Giirke. 
Synopsis der Mitteleuropdischen Flora (1896 — ), i, ii, iii, iv (part), and vi, by Ascherson and Graebner. 
The standard floras of various countries of Europe and of the U.S.A. t 
In the case of naturalised exotic species, we have consulted the floras of those countries 
in which these plants are indigenous, e.g., Flora Capensis , Flora Australiensis, and other works 
issued by the authorities at Kew. 
A Ititudes 
The figures as to the altitudes reached by plants in the British Isles are largely obtained 
from various local floras and partly from a paper by Mr F. N. Williams on The High Alpine Flora 
of Britain (in Ann. Scott. Nat. Hist. (1908 — 1910)), whilst those relating to the altitudes reached 
on the mainland of Europe are largely obtained from Die Farn- und Blutenpflanzen von Tirol , 
Vorarlberg, und Liechtenstein (1902 — ) by v. Dalla Torre and v. Sarnthein, from Ascherson and 
Graebner’s Synopsis ( op . cit.), and from various monographs and papers by P. Jaccard, E. Riibel, 
H. S. Thompson, F. N. Williams, and others. 
The Channel Isles 
We include the Channel Isles within the limits of the British flora, though in no real 
geographical sense may this legitimately be done. Still, it has been usual to include the Channel 
Isles in British floras; and, on the whole, we think it desirable to continue to do so. There 
are only a few species which occur in the Channel Isles and not in the British Islands, scarcely 
more, e.g., than occur in Cornwall and the west of Ireland, whilst any Sarnican and non- British 
plant may at any time be discovered in the extreme south of Great Britain. The inclusion of 
such Sarnican species therefore in a British flora at least serves as a stimulus to British field- 
botanists, besides satisfying the natural desires of the English-speaking botanists of the Channel 
Isles themselves. 
Citizenship of species 
We have decided not to use the terms invented by H. C. Watson to denote the various 
grades of citizenship of British plants. The terms which Watson used are “native,” “denizen,” 
“colonist,” “casual,” and “alien.” Of these, the term “denizen” has as often been used as 
synonymous with “ alien ” or at least “ naturalised alien ” as in the sense actually laid down by 
Watson; and it is, in our judgment, impossible in practice to differentiate between “colonists” 
and some “casuals,” and between “casuals” and some “aliens.” We have preferred to state 
the facts of distribution in simple language rather than to obscure the facts by the use of ambiguous 
terms. 
The conspectus 
We do not furnish any analytical or artificial keys to the groups of plants. These keys 
are scarcely ever satisfactory. We endeavour to assist the student in classifying his plants by 
setting forth, under each group, a conspectus of the more important characters of the groups 
of the next lower rank, and in giving (wherever the exigencies of book-production allow) 
a reference to the page where the lower group is considered : when no cross-reference to a page 
is found, it is necessary to consult the Addenda or the index. By following the groups and 
sub-groups in this way, it is hoped that the student will be able to identify the indigenous 
and established wild plants of the British Islands. 
Cambridge. 
December 24th, 1913. 
C. E. MOSS. 
