VEGETATION OF BLAKENEY POINT. 
505 
bushes, which, at the surface, stem the tide of the advancing 
shingle.' 
The presence of the Suaeda bushes converts the surface into 
a partially stable crust, but apart from the movement forward 
of the upper layers of the shingle, there is perhaps also a bodily 
movement derived from the wave impact through which the 
underlying portions of the shingle are driven forward beneath 
the partially stable crust as if of semi-fluid consistency. So 
that the bank as a whole advances even though the surface in 
parts remain stable, and its vegetation undisturbed. The im- 
portance of this groyne action as a factor bearing upon the 
vegetation is well seen on that part of the main bank which lies 
between the dunes of the Headland itself and those which con- 
stitute the Hood. Along this stretch of shingle large quantities 
of drift accumulate, but the Suaeda bushes are situated low 
down on the flanks and are no longer to be found on the crest. 
The shingle is thus relatively mobile, but though at the same 
time well fed with drift, we nevertheless find associated with 
these conditions a sparse vegetation in which the dominant 
species are those like Glaucium, Sedum and Rumex trigranu- 
latus, which readily arise from seed. Of these plants, Sedum 
and Glaucium, though potentially perennial, frequently behave 
as biennials. This is most strikingly the case with Sedum 
which, though present in abundance one year, may completely 
die away to be replaced by seedlings, so that in the year 
following the maximal region has shifted elsewhere. On the 
landward slopes and in other protected situations, Glaucium is 
usually perennial, but on and near the crest the bulk of the 
individuals do not survive the flowering period. On the old 
sterile portions, Glaucium, Rumex and Sedum are wanting or 
very rare, and it would seem from this that drift is to them a 
prime necessity. 
The results of cultures of Rumex trigranulatus bear out this 
hypothesis. Pots were for this purpose filled with shingle 
7. Prof. Oliver informs me that in December, 1912, a high tide had been over 
the main bank, which by its effects shewed clearly this groyne action of the 
Suiedas ; where the waves had had an uninterrupted run the shingle was smoothed 
out as by a steam-roller, and the level often raised (as indicated by the burying of 
the Euinexi qu.tie stx inches. 
