THE BROWN SEAWEEDS OF THE SALT MARSH. 367 
The Cryptostomata of Fucus vesiculosus megecad limicola. 
The prominence of cryptostomata and their marginal position is a very 
marked feature of the salt-marsh varieties of F. vesiculosus. These curious 
organs are also very prominent in the marsh F. ceranoides. We have not 
been able to examine the question of the cause of this in detail, but probably 
future work may throw some light on their function. It is, however, to be 
noted that, in Fucus vesiculosus, the cryptostomata increase in relative size 
and frequency and become more and more strictly marginal in position as 
the habitat becomes more exposed. Their presence in great abundance is a 
criterion of a faculty for the endurance of prolonged exposure, both in rock 
and marsh forms. 
Application of these Principles to the Morphology of the 
Loose-lying Fuci of the Baltie. 
In the Baltic Sea three dwarf forms of Fucus vesiculosus form the chief 
constituents of one of the loose-lying formations characteristic of sheltered 
lagoons in that tideless sea. These have been described in some detail by 
Svedelius (1901), whose work upon them has been summarized in a previous 
paragraph (Part 1, p. 338). In form they approach closely to the ecad 
cæspitosus of the limicolous Fucus vesiculosus ; but at first sight their habitat 
seems to have very little in common with the salt-marsh habitat. They occur 
in large masses quite unattached, on the sea-bottom, at a depth of 8-10 metres, 
in places where there are no currents. 
Their most striking morphological peculiarity is their extremely dwarf 
habit. We have seen that in the marsh Fucoids a dwarf habit is correlated 
with increased exposure by the tide, In this formation the reverse change 
has happened and the plants are never exposed. In spite of this the change 
in essential physieal conditions is not wholly dissimilar. We know too little 
about the physiology of the Fuci to say what “exposure " or its concurrent 
consequence—a shortened immersion in sea-water—means. In the case of 
marsh Fuci we were able to unravel one of the complex of possible factors 
operating in “ exposed ” conditions and to show that the narrowing of the 
thallus was directly attributable to a decrease in the access of nutrient salts, 
brought by the sea-water. In the Daltie loose-lying formations the same 
factor operates from a different cause. The salinity of the Baltic Sea is low 
in the first place, and in the second place the stillness of the water about the 
loose-lying alge prevents their using the salts from any but the actual water 
they оссиру. This lack of nutrient salts then explains the extreme tenuity 
of the Baltic forms, which may reach filiform dimensions. Svedelius (1901, 
р. 85) considers the narrowness of these forms to be due to the incessant lack 
of the new recruiting forces of sexual reproduction in the loose-lying forms ; 
so that “the broadest loose-lying forms are those which last altered their 
