Fen Plants 221 



whole together, form a dense mass of vegetation which shelters 

 and shades the Lastraea and Jungermannia. 



It should be noted, however, that what has been called the 

 wet group is only to be found as a group round the skirting 

 ditches and is best developed on the western edge of the fen. 

 In these places where the ground is subject to frequent in- 

 undation the Phragmites ousts the Cladium; elsewhere, where 

 flooding is of rarer occurrence, the Cladium, being better able 

 to resist the drought, drives out the Phragmites. While it is 

 not usual to find those species mentioned under the dry 

 group encroaching upon the wet belt, yet the "wet plants" 

 may frequently be found among the plants of the dry group. 



It seems probable that the two transition zones of vege- 

 tation already mentioned, depending as they do upon water- 

 supply, will be able to be traced round the fens. They occur 

 at Chippenham Fen, and from near Mildenhall to Lakenheath 

 in Suffolk, in some places better, in other places not so well 

 marked, as on the western side of Wicken. 



Although their characters are roughly the same in these 

 places, rough meadows and what has been called moor, their 

 plant associations vary in the first place with the soil, and 

 secondly with human influence. At Chippenham, for instance, 

 the chalk uplands masked with loose sand are almost entirely 

 under cultivation, but their lost flora can be reconstructed 

 from similar hill-sides in Suffolk. The meadow-zone yields 

 such chalk plants as Blackstonia perfoliata and Gentiana 

 campestris, while the moor is a Rush and Carex association. 

 These two zones pass one into the other, the whole forming a 

 gentle slope ending in the fen which resembles Wicken in its 

 abundant growth of Cladium and Molinia, 



Along the Suffolk border the slope is more gradual than at 

 either Wicken or Chippenham. The upland flora is for the 

 most part undisturbed, but will be referred to later ; the tran- 

 sition zones are much entangled. The dominant plant in the 

 first is Saxifraga granulata. This either covers the field with 

 a sheet of white or occurs in local patches, according as the 



