408 Salisbury . — The Soils of Blakeney Point : A Study of Soil 
As the acidity and organic content of the soil both rise with increas- 
ing age of the dune system, the influence of rabbit droppings, either as 
regards the amount of organic material added, or the soil reaction, is 
evidently of quite minor importance. Rabbit faeces are, however, of con- 
siderable significance in the water economy of the dune plants, as is shown 
by the frequency with which copious development of fine roots is often 
associated with their presence. 
The Influence of the varying Soil Conditions on the Dune Vegetation. 
The stages in dune succession have been shown to present a graduated 
series of conditions with increasing age ; an edaphic succession in fact in 
which mobility, low organic and* water contents, high calcium content, and 
a neutral or alkaline reaction mark the earliest phases, whilst the final 
phases present a stable soil, a high organic content, relatively high water- 
content, a total absence or negligible quantity of calcium, and an appreciable 
acidity. The adaptation of the pioneer species to mobile soil, the stimulated 
growth they exhibit when buried by further accretion, are facts so well 
known as to require no emphasis here. The stabilizing action of the plant 
covering, which enables less specialized species to become established, is also 
not only familiar but underlies the elaborate technique of dune maintenance 
and protection. The calcium content and reaction of dunes have, however, 
received but little attention, and it is upon the influence of the changes in 
these that we would lay particular stress. 
The writer has elsewhere pointed out (‘The Significance of the Calcicolous 
Habit’, Journal of Ecology, vol. viii, pp. 202-15, 1920) that the plants 
normally characteristic of soils rich in calcium probably occur on such, 
either on account of their preference for bases or because of the dry 
character of these soils. The data here given show that both conditions 
are satisfied in the younger dune phases, and hence we might reasonably 
expect to find something in common between the flora of the chalk and 
that of the ‘ yellow ’ dune. 
There is reason for suspecting that some of the pioneer species, such 
as Psarnma arenaria , Elymus arenarius , Agropyrum junceum y Euphorbia 
Paralias , &c., are somewhat partial to a calcium-rich medium and may 
perhaps be ‘oxyphobic’, but their specialization to a mobile substratum 
precludes the expectation of their occurrence on chalk downs and, similarly, 
we should not expect to find representatives of the calcareous pasture on 
the extremely mobile soil of an embryo dune. The edaphic conditions of 
the later phase of the yellow dune are those where we should look for the 
resemblances indicated. 
Actually no species especially characteristic of the chalk flora are met 
with on the Blakeney Point dune system, but elsewhere in this country 
and in other parts of Europe the calcicole element in the dune flora is 
