THE BROWN SEAWEEDS OF THE SALT MARSH. 331 
1. The Blackwater Fuci. 
In the marshes of the River Blackwater (shown in sketch-map, Pl. 30), 
one of the original localities for the Fucus volubilis of Hudson, the Fuci are 
abundant and show a great range of form. We made a series of collections 
from these marshes, from which we found :— 
(1) That the varieties could be arranged in a single series, leading by 
gradual transitions from short, narrow, turf-like forms, showing no spirality, 
A 
Fic. 2.— Fucus vesiculosus megecad limicola. Nat. size. 
Showing transitions from the ecad cæspitosus, A, В, С, D, to the ecad volubilis (with one 
vesicle), б. Е. Fruiting specimen. Blackwater Marshes, Essex. 
to large forms with much spirality and the general habit of Fucus vesiculosus, 
L. (such a series is shown in text-figs. 2—6). 
(2) That, in the intermediate forms, the presence or absence of vesicles is 
correlated with no change either in habit or distribution (see text-figs. 4-6). 
(3) That the modifications in form could be directly correlated with the 
habitat in every case (see Part 2). 
(4) That receptacles when present were dicecious, and these were found 
on all but the smallest varieties. Fig. 2, Е, represents the smallest specimen 
found fruiting on these marshes. 
For these reasons we inferred that all the Blackwater Fuci were derived 
from a single parent, Fucus vesiculosus. 
