Phytogeogr apical Excursion in the British Isles. 273 
part in the choice of route and in the general arrangements. 
Professor Chodat of Geneva, also conducts distant excursions for 
his students once or twice a year. 
The rise and spread of the study of vegetation which has been 
so marked a feature of recent years, demands, even more urgently 
than floristic botany, the organisation of expeditions of this kind. 
While the student of the distribution of species can depend 
more or less on herbaria and on floras, which at least give him 
systematised, though often inadequate, information as to the species 
of plants which occur in other countries, the student of the distri¬ 
bution, structure, relationships and development of plant-com¬ 
munities has to depend upon published descriptions and photo¬ 
graphs of vegetation, which, even at the best, do not convey to 
him an idea of the phenomena involved in any way comparable 
with that which he can obtain on the spot, especially with the 
assistance of botanists who have actually studied the vegetation in 
question. In the present somewhat rudimentary state of evolution 
of the concepts and corresponding language of ecological plant- 
geography, this difficulty of obtaining clear and definite ideas of 
the vegetation of other countries without visiting them is 
necessarily very great. Workers in different countries use different 
names for the same thing and the same name for different things; 
they are frequently not at one as to the fundamental differentia of 
the units they employ. When we add to the difficulties arising on this 
score the fact that while vegetation all over the earth has, beyond 
question, fundamental similarities in regard to its structure, 
differentiation and relation to habitat, yet these similarities are 
greatly obscured by certain peculiarities of climate, soil, and floristic 
distribution, and even more by the results of the long-continued 
activity of man in the countries which have an old civilisation, it 
is not surprising that, with the best will in the world, keen students 
of vegetation in different countries should often altogether mis¬ 
understand one another’s writings. 
To overcome such difficulties much patience and determination 
and frequent interchange of visits are absolutely essential. It was 
with the object of making a definite beginning in this direction 
that the British Vegetation Committee, at the suggestion of the 
present writer, decided, in December, 1908, to attempt to organise 
an international excursion in the British Islands, “than which” to 
quote the words of the preliminary circular issued in January, 1910, 
“ it is believed there is no easily accessible European country less 
