THE BROWN SEAWEEDS ОЕ THE SALT MARSH. 355 
PART 2. 
THE RELATION OF THE PHYSICAL FACTORS IN THE SALT MARSH HABITAT 
TO THE PECULIAR MORPHOLOGY or LimicozLous Fucorps. 
THE ESSENTIAL DIFFERENCES BETWEEN THE Rock AND SALT-MARSH 
HABITATS. 
It was first of all necessary to find out whether an embedded Fucus could 
translocate water from the soil to the subaerial parts of the plant. This was 
done by potting up a series of blocks of marsh-mud with embedded Fucus 
vesiculosus еса volubilisand keeping the ground soaked with sea-water, while 
the shoots resting upon the surface were not wetted, It was found that, 
after about a week or ten days, the subaerial parts of the plants withered 
away and dried up close down to the ground, while the buried parts of the 
thallus were perfectly vigorous. Evidently no effective translocation of 
water can take place from the underground parts of the thallus, and it is 
probably quite safe to assume that the embedded parts of a marsh Fucus are 
simply and solely an anchorage to the plant. 
‘Che first important difference between rock and marsh is the small vertical 
range of the marsh. This is illustrated by the diagram (fig. 14, p. 363), which 
has been compiled from data obtained in several localities. The levels measured 
have been taken in reference to an August spring and пеар tide in each 
locality, and then reduced by simple proportion to the values they would 
have shown under а 13-foot August spring tide. They serve rather as an 
illustration than as a record of fact. The whole of the salt marsh is between 
high-water of пеар tides and high-water of spring tides, although on the 
banks of channels Fucus vesiculosus ecad volubilis may extend considerably 
lower. "This forms a narrow zone, corresponding on the shore to the zone 
occupied by Pelvetia and Fucus spiralis, or the uppermost zone of the rock 
Fucoids, and it means that the algæ are exposed for a period of several days 
every fortnight, a novel condition only to those algæ occupying the lower | 
levels of the shore. 
The factor which makes the salt marsh habitable to the species which 
naturally oceupy the lower zones of the shore is no doubt the relatively high 
humidity, maintained throughout the long periods of exposure partly by 
evaporation from the wet, ill-drained soil, and, still more, during the summer 
months, by the transpiration of associated phanerogamic halophytes. 
A second consequence of the conjunction of algæ as undergrowth with 
halophytie vegetation is the shade afforded by the leaves and shoots of the 
higher plants. Probably on account of this, marsh alge often show deep 
rich colouring. 
