Phytogeographical Excursion in the British Isles. 17 7 
VIII—Some Impressions and Reflections. 
By F. E. Clements (Minneapolis). 
S one of those deeply interested in the structure and develop¬ 
ment of vegetation, I shall leave to other members of the 
party the difficult but pleasant task of doing justice to scenic 
Britain and to British hospitality. I shall confine myself to 
sketching the kaleidoscopic impressions of British vegetation, with 
an occasional reference to the interpretations arising out of 
comparisons with American vegetation. 
The three days spent in the Norfolk “Broads” revealed the 
general features of a fascinating succession with an unusual 
number of structural and developmental problems. The striking 
alternation of Scirpus , Typha, Phragmites and Cladium affords 
unique opportunity for the study of their habitat equivalences and 
re-actions. It would be difficult, if not impossible, to find a region 
quite so favourable for such work, owing to the labyrinthine nature 
of the “ Broads,” beside which the fabled labyrinths of Crete seem 
mythical indeed. In the case of the submerged and floating 
populations, the light and aeration factors furnish an almost 
untouched field, while on the other side, historically, of the reed- 
swamp plexus, stretch the problems of its conversion into fen and 
carr. The ecotone between swamp and fen is an unusually broad 
one, with corresponding possibilities for studying the change of 
dominance in relation to habitat factors. 
At Blakeney, the vegetational interest centred in the sharp 
contrast between the salt marshes and the shingle beach, which 
both makes the marshes possible and then overwhelms them. As 
a dynamic center, the shingle bank is rivalled only by the sand 
dunes, though it seems to differ in being rather more periodic than 
continuous in growth. The production of new habitats for coloni¬ 
zation rarely occurs in such a rapid manner, while the periodic 
development of lateral banks would seem to furnish a unique basis 
for the study of the sequence of different populations, both 
on shingle and in the marsh. The quantitative study so charac¬ 
teristic of British ecology, finds perhaps its best exemplification at 
Blakeney, where also the refinements of exact methods can be 
carried further than in more complex regions. 
English woodlands are an intricate puzzle to the American 
