THE BROWN SEAWEEDS OF THE SALT MARSH, 377 
ecad cwspitosus, was therefore suggested for the dwarf turf-like form, 
commonly known as Fucus balticus ; while for the other marsh forms of 
К. vesiculosus, the names ecad volubilis and ecad museoides were retained. 
А detailed study has been made of the connection between the novel 
physical factors, operating in the salt-marsh habitat, and the morphological 
modifications, characteristic of that environment. Two general methods have 
been employed in this investigation :— 
(1) An examination of the distribution of the natural varieties of a single 
salt-marsh species, from which the effect of variations in certain physical 
factors upon that species has been deduced. 
(2) А critical examination of the conditions under which exceptional 
forms may be produced which do not show the usual salt - marsh 
modifications. 
By the combination of these two methods a certain amount of evidence 
has been brought forward, correlating the morphology of these forms with 
their new environment. The results may be stated in epitome. 
Dwarf Habit is due to a change in the vertical position of the species 
relatively to the tide. This eauses prolonged exposure, which produces a 
shortening of the thallus, together with a decreased access of nutrient salts, 
which produces a narrowing or attenuation of the thallus. 
Curling or Spirality is probably due to an unequal distribution of water and 
nutrient salts upon the thallus, which is spread out over the mud in inter- 
tidal periods and inappreciably moved by the covering tides; but this quality 
is of great advantage to a marsh alga and may be promulgated by selection. 
Vegetative Reproduction, or the replacement of vegetative budding for 
sexual reproduction, is probably favoured by the humidity, maintained over 
the marsh surface in the intertidal periods. This prevents the cell-sap from 
reaching а certain limiting concentration, which is necessary as a stimulus 
for the production of receptacles and, further, for the maturing of the sexual 
bodies. The subject is beset with many difficulties, not the least being that 
the formation of sexual organs appears to become habitual after a preliminary 
series of stimuli. The formation of vegetative buds may be favoured by the 
high humidity in the intertidal periods. 
A consideration of the conditions operating in the loose-lying Fucaceous 
formations of the Baltic, showed that similar changes in morphology were 
induced by the same change in physical conditions, with this one difference, 
that the shortening of the thallus, associated on the salt marsh with the 
vague term “exposure,” is referable, in the loose-lying formations, to a 
decrease in the photosynthetic activities of the Fuci, caused by diminution 
in light and СО» access. 
Ап examination of the morphology of the famous floating Sargasso weed 
revealed the interesting fact, that its peculiarities could be referred to the 
