228 The Breckland 



the Little Ouse and Lark Valleys next the Fenland, and upon the blown 

 sand between the large blow-out on Lakenheath Warren and the village 

 of Santon Downham. But it is widely distributed in small and large 

 patches, and it grows, although it does not necessarily become dominant, 

 on all the seven soil stages. 



Light has been thrown on this interesting distribution by Mr C. E. M. 

 Tidmarsh," of the Botany School, Cambridge, who has shown that for 

 the successful germination of the seeds a continuous 12 to 20 days' water 

 supply (depending on the temperature) is necessary, and that for the 

 successful estabhshment of the seedhngs similar moist conditions are 

 needed. These requirements hmit the estabhshment of Carex to the neigh- 

 bourhood of water — of rivers like the Lark and Little Ouse, of meres, or 

 of temporary (but not too transient) bodies of water appearing in lower- 

 lying parts when the water table is high.^ Even if these conditions are 

 satisfied, the estabhshment of a seedling wiU be checked by rapid recession 

 of the water table leaving the soil too dry for its survival: thus temporary 

 water-logging offers a somewhat precarious start for Carex, 



From these points d'appui, Carex spreads to soils that are essentially dr}\ 

 The recognition of its early behaviour (the retention by seed and seedling 

 of needs that once may also have characterised the adult), not only explains 

 much of its distribution on Breckland, but also its development on sand 

 dunes near the coast, where it becomes established first in the slacks and 

 later spreads to the dunes. Once established, it spreads freely by rhizomes, 

 and most successfully on loose soil. There are, however, patches of Carex 

 in Breckland whose relation to a place suitable for its establishment is not 

 clear. These may be scattered vestiges of a former continuous area in which 

 retrogression has taken place through the activity of rabbits. Just how far 

 Carex may degenerate, like Calluna and Pteridium, without the help of 

 animals like rabbits and mice, is not known. Its behaviour on sand dunes 

 along the coast certainly suggests a loss of vigour with age, but whether 

 this proceeds to the point of annihilation in small or large patches is not 

 yet determined. 



The varying height of bracken from year to year; the changing density 

 o£ Agrostis; the results from the apphcation of water to Agrostis during dry 

 years; the negative results obtained during the abnormally wet year 1937; 

 and the periodic phenomena already described — all these suggest a causal 

 relation with climate and, in particular, with the rainfall. There is abundant 

 evidence suggesting that scarcity of water is a major difficulty to plant hfe 

 in Breckland. But the relation between the cyclic phenomena and rainfall 



' In unpublished work. 



* As, for example, in the spring of 1937 after a long wet speU. 



