95 
The Shingle Beach as a Plant Habitat. 
with interesting results. Thus, to the west of the Martello tower 
at Rye Harbour the Common Stinging Nettle ( Urtica dioica) has 
become widely dispersed, and eventually the bare shingle banks 
are completely transformed into verdant, grassy lawns. The 
method is as follows. The Nettle establishes itself in a narrow 
zone at the foot of the bare bank and slowly works its way up to the 
summit. In its immediate wake a closed association of fine grasses 
follows, flourishing on the ground prepared for it by the decay of 
the nettle-rhizomes. The last stage shows the nettles arrived at 
the top with the grass choking them out. Their work is finished; 
the only useful work in Nature I ever saw the Nettle perform ! 
When apposition banks are formed on any considerable scale, 
they become of course relatively remote from the sea. This 
probably makes them climatically different from the other types of 
bank, and taken in conjunction with the undulating nature of their 
surface, perhaps explains the comparative readiness with which 
shrubs and even trees spring up upon them. Characteristic of 
these may be mentioned Rubus, Ulex europceus, Cratcegus and 
Sambucus nigra. 
This brief epitome of shingle habitats will suffice to show that 
much information has yet to be collected and compared before 
even a provisional treatment of the vegetation is possible. The 
more obviously distinct types of habitat in respect of the physical 
conditions are (1) the crest and storm shelf; (2) the back and 
buttresses; (3) the terrace (dormant parts) ; (4) the terrace (mobile 
parts) ; (5) the hooks; (6) the apposition hanks. 
As regards the plants themselves, the question is sometimes 
raised as to whether there are any real shingle plants apart from 
the numerous invaders from the salt-marsh, the plants of sandy 
ground, and the ruderal plants so commonly found. 1 How this 
may be I hope to consider on a future occasion. It may be 
remarked, however, that not a few of the apparent anomalies of 
plant-distribution on shingle banks find their explanation when it 
is realised that their distribution is determined not by the shingle 
but by some other factor. The case of Arenaria peploides is a good 
illustration. This plant forms extensive mats over a large part of 
the back of the Blakeney Bank, though there are certain stretches 
from which it is conspicuously absent. On the Hurst Castle bank 
it is very rare, and it thrives badly and only in small quantities on 
the Calshot Spit. Only a single specimen was detected on the 
' Cf. A. G. Tansley. “Types of British Vegetation,” p. 353. 
