VEGETATION OF BLAKENEY POINT. 21 



bushes, which, at the surface, stem the tide of the advancing 

 shingle. 7 



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 trigvanu- 

 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 

 Susedas; 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 Rumex) qu.tje six inches. 



