Reaction and Succession in Relation to the Plant Covering. 4 1 1 
The Lateral Shingle Beaches. 
From the point of view of edaphic succession it must be borne in mind 
that the main shingle bank throughout its entire extent is more or less 
subject to (a) addition of new material, (b) removal of material from the 
sea-face landwards, (c) submergence by excessively high tides bringing with 
them new supplies of organic material and carbonates in the form of shells. 
These conditions maintain the main beach in a more or less juvenile state, 
so that the natural changes which might be anticipated with the lapse of 
time tend to be masked. 
The instability of the shingle is considerably diminished by the 
presence of Suaeda bushes, and where these are most numerous, viz. 
opposite the marrams, the largest number of species and the most extensive 
carpet of vegetation anywhere upon the main shingle bank are met with. 
The importance of this lack of mobility is further emphasized by the 
location of certain species, e. g. Convolvulus soldanella in the neighbourhood 
of the Suaeda bushes, with every indication of having spread from these 
latter as their centres of origin (cf. F. W. Oliver, ‘ The Shingle Beach as 
a Plant Habitat’, New. Phyt., vol. ii, pp. 73-99, 1912, and Oliver and 
Salisbury, ‘Vegetation and Mobile Ground’, Journal of Ecology, vol. i, 
pp. 249-72, I 9 I 3 )* 
The lateral hooks still further emphasize the great importance of the 
degree of mobility. These are for the most part extremely stable and 
present in their older phases a continuity of vegetation which is never 
attained on the main bank itself. 
Each lateral bank represents a landward deflexion of an original 
termination of the main bank, which latter subsequently continues its growth 
in a sympodial manner. 
The interval between two successive laterals is thus an indication of 
the time interval between the violent storms during which the laterals are 
formed. The latter, owing to the continued growth of the main beach, are 
relatively sheltered, and this protection is increased with the formation of 
each new lateral (cf. Oliver, ‘ The Shingle Beach as a Plant Habitat ’). 
Mechanical A nalysis and Mobility. 
Perusal of the data in Table X respecting the mechanical analysis of 
the successive shingle laterals into coarse and fine particles shows that the 
proportion below 0*5 mm. in diameter increases with the increasing age 
of the shingle bank, the lowest values being obtained in samples from the 
main beach. The oldest laterals have indeed nearly seven times the pro- 
portion of fine particles present in the shingle of the main beach. 
It will be noted that both the observed range and average for the 
oldest lateral but two (Bank III) is higher than for the oldest lateral itself. 
