278 BRITISH PLANTS 
1. Flora of Mud-Flats and Salt-Marshes.—On the muddy 
margins of estuaries, and in low-lying ground liable to 
periodic floods from the sea, the soil is saturated with salt- 
water, and the plants are typical halophytes, with fleshy ~ 
leaves or stems (p. 88). 
Usually submerged in the water of the estuary is a 
zone of Zostera, and above this, on the flat reaches, wholly 
or partially submerged at 
high tide, the only vegeta- 
3 tion consists of Salicornia 
im herbacea (annual glass- 
i q 4 wort), or in some parts 
ML | OA S. radicans (perennial). 
o ra He These may form a thick 
We bee sward if the mud is only 
= QV WW just covered at high tide, 
> WS OAD but when the water is 
Soa  \ ‘an 
WIESA WA" deeper the plants stand 
=O Ly A fi far apart. The Salicornias 
SAY/ *\ AY have fleshy green stems 
“ Wy ie and minute, adpressed, 
ce Y H 4 enedilet le 113); 
‘NA \\ 4 AW the cell-sap is highly con- 
ae & SAN a centrated, and in every 
way the plant is excellently 
= 
“Sal adapted for life in this 
pi} extreme xerophytic en- 
DB vironment. Salicornia is 
Ze the first inhabitant of the 
mud - flat, and sediment 
brought down by the river 
i is caught at the base of 
a the plants. As the mud 
Fig. 113.—Salicornia herbacea accumulates, the flat be- 
pred iea g Ab (AFTER comes higher and drier, and 
other plants now begin to 
colonize the ground. The earliest of these new-comers 
are Glyceria maritima and Triglochin maritimum, which 
sometimes form a distinct zone above the Salicornia. 
Out of reach of the highest tides the general salt-marsh 
flora develops. The vegetation is frequently of two 
types. In the wetter parts a salt reed-swamp develops, 
characterized by monocotyledons with erect, narrow leaves, 
