296 Matthews .— The Distribution of certain 
especially dealt with. Arabis stricta , Huds., Dr aba aizoides , L., Dianthus 
caesius, Sm., Euphorbia stricta , L., E. pilosa , L., Cephalanthera rubra , Rich., 
Allium sphaerocephalum } L., Car ex tomentosa , L., and Koeleria vallesiana 
All. belong to this western group. The first only is western in Europe, 
the others being generally distributed throughout the Continent. Their 
localization in Britain is difficult to understand unless it is the result of 
chance introduction, although it may possibly be due to an extension of 
that movement which has helped to build up the peculiar element in the 
Peninsula flora. 
Yet, of the total number of ‘English’ species, only 12 per cent, lie 
outside the coastal counties from Cornwall to Norfolk. That 88 per cent, 
should occupy this belt and gradually thin out inland seems strong evidence 
that immigration has been, on the whole, a fairly definite movement. The 
process has doubtless gone on for thousands of years, and while occasional 
introduction may have been the general event, the chances would seem to 
be in favour of plants reaching points near or having some relation to their 
chief continental centres. The process may thus approximate to a definite 
tendency, and we might predict, as is often done, where certain species are 
most likely to occur. But not infrequently plants will be carried out of and 
beyond the general trend. They are the particular cases which do not 
follow the general rule nor conform to the general law. We have seen that 
in the * English ’ portion of the British flora they are relatively few in 
number. 
Summary. 
A brief survey of the divergent views held regarding the origin of the 
British flora is given, and the source and distribution of 266 species which 
are restricted to England and Wales are then considered. A map illustrates 
the range of these species, and the general conclusion is reached that this 
limited portion of our flora has been derived mainly by advance through 
France in post-glacial times. A detailed analysis shows that nearly 50 per 
cent, of the group is of great rarity. Excluding some 30 species which are 
boreal or western outliers (some as relics of a former arctic-alpine flora, 
others possibly as recent introductions), this rare element is centred along 
a coastal belt from Cornwall to Norfolk. Certain areas of concentration 
are found to exist indicating, it is believed, points of arrival and establish¬ 
ment rather than areas of retirement. These features provide a clue to 
invasions, and details are given for four small assemblages which may be 
regarded as having followed different migratory paths. An invasion from 
the east and another from the south are distinguished, and between these 
two lines the main portion of the English flora has probably advanced. In 
addition to the cartographic studies presented, the results are expressed in 
