A SURVK.Y OF THK LOWER TEKS MARSHES 1 27 



and estuaries, and though the phenomena awaiting elucidation 

 here must perforce be of the same order as those studied else- 

 where, the local problems offered by the peculiarities of 

 Greatham Marsh and its distance from the sea form a rich 

 field for work more intense than war conditions have allowed 

 me. 



Owing to the enormous length of time the main bulk of the 

 marsh has been established within its present bounds, to a 

 first glance no scope is given for the observation of the plant 

 successions. Fortunately, all the necessary steps in the pro- 

 cess of colonisation can be observed on the mudbanks and 

 spits characteristic of the Creek and drainage channels, as 

 well as on mud deposited when a high tide silts up a 

 depression. In an equally satisfactory fashion, the developing 

 secondary marsh yields material for the study of a certain 

 phase of retrogressional movement. 



Whether the bare ground offered as a site suitable for 

 occupation is a muddy spit or a sandy scour, the very first 

 colonists are green algae oi the gtntxa. Rhtzoclonium, Vaucheria 

 and Chaetomorpha, which not only form a favourable sub- 

 stratum for holding germinating phanerogams, but also have 

 much value as soil binders. Deliberate tests to estimate 

 their consolidating value were made by dragging up a hand- 

 ful ; an astonishing amount of mud was lifted with them. 



As soon as the ground is suitable ■5'rt/zV^/7«iz(f appear in huge 

 numbers, forming an open Salicornietum europaeae. Whether 

 by chance or as a direct effect of the environment, I noticed 

 that the invading hosts on the sandier ground tended to 

 belong to the red form, whilst on the muddier, and possibly 

 saltier tracts, the apple green variety prevailed. Against the 

 view that colour and soil are correlated, can be advanced the 

 fact that at minor stations, where colonisation is proceeding in 

 the general area of the marsh, the colours form a mosaic of 

 red, purple, and green. Viewed in its proper light, this latter 

 fact would seem to suggest that the dominant colour in 

 isolated assemblages depends essentially on the circumstance 



