THE BROWN SEAWEEDS ОЕ THE SALT MARSH. 359 
are characteristic of an exposed habitat; here compare aiso Cotton’s in- 
teresting account of the short varieties of Fucus ceranoides, about 1 in. only 
in length, occurring at the Pelvetia level in the Newport River (Clare 
Island Survey, 1912, p. 85). 
Although these deductions probably hold in a general way, there are no 
doubt other factors which must be taken into account in special cases. For 
example, the most minute form of Fucus vesiculosus megecad limicola, the 
ecad muscoides (Cotton), is characteristic of peaty marshes, and it is possible 
that the acidity of the soil has a further dwarfing effect on the plant. 
Arcichovskij (1905) finds that the contamination of water with organic 
debris (e. g. in the Kiel Canal) leads to a dwarfing of the Fuci. 
(д) SPIRALITY OR CURLING. 
[t has been difficult to obtain direct evidence correlating the curled, twisted, 
or spiral habit, shown by practically all marsh Fucoids, with any special 
Fra. 12.—Fucus vesiculosus proliferations experimentally produced on the Samphire Marsh, 
Blakeney. Nat. size. 
factors in their new habitat ; this is largely because the contortions of these 
plants are a very constant character, and where variations occur they are 
not so directly influenced by changes in physical conditions as the variations 
in size which have just been under discussion. This is illustrated by the 
two specimens of Fucus vesiculosus еса volubilis (figs. 4 & 5, pp. 933 & 334), 
which were found interwoven in the middle zones of the Blackwater marshes, 
and yet show a great difference in spirality. 
TI . А ` ] - . К | LI LJ . . LI b . ni t 
rere were, however, two conditions in which spirality in Fuevs vesiculosus 
megecad limicola became markedly reduced. The first was under low con- 
centration of salt water, as shown in the attenuated forms (fig. 15, р. 366) ; 
the second on the assumption of the upright turf-like habit, as in the 
ecads ecspitosus and muscoides. Similarly, the turf-like Pelvetia canaliculata 
2c2 
