MUD-FLATS 17 
that it is colonized by minute Lichens, many of which 
have the power of dissolving the limestone, produc- 
ing tiny burrows in which they live securely. 
On the sands and mud-flats a semi-desert exists, 
due in great measure to the shifting nature of the 
material and the difficulty which plants find in secur- 
ing an anchorage in it. But in the upper parts, near 
high-water mark, a few land plants—notably the 
Glasswort (Salicornia europea, Fig. 2), a fleshy little 
a. 
Fic. 1.—A BuRROWING LICHEN (VERRUCARIA CALCISEDA), 
LIVING IN LIMESTONE, 
a, Natural size; 6, greatly enlarged; c, section, greatly enlarged. 
annual—colonize the dreary flats with tiny forests of 
dark green branches, and lower down many small 
Seaweeds flourish. Some of these, ramifying through 
the surface layers, help to bind together the shifting 
sand, and by entangling in their branches fresh par- 
ticles, and by continued growth, tend to raise and 
consolidate the surface, to render it suitable for the 
immigration of land plants such as the Glasswort, 
and thus eventually to reclaim it from the sea. 
2 
