328 DR. SARAH M. BAKER AND MISS М. Н. BOHLING ON 
Most systematists regard these six species as thoroughly well established, 
despite the fact that many varieties are known of the four Fuci, which 
show transition forms, connecting the species. Recently, however, the 
validity of the three species, F. spiralis, ceranoides, and vesiculosus, has been 
questioned ; first, by J. Chalon (1904-1905), and, later, by Stomps (1911), 
who has collected a mass of interesting evidence in support of his contention 
that they are to be regarded as adaptational varieties of one species. 
It is well to restate the fundamental distinctions between the species. 
Between Fucus spiralis and vesiculosus the only reliable diagnostic character 
is that the former is hermaphrodite and the latter dicecious. When present, 
the round hard vesicles of F. vesiculosus are peculiar to that species ; but 
they should not be confounded with irregular, soft, blister-like swellings, 
which appear frequently on all three species, especially in brackish water. 
F. ceranoides may be either hermaphrodite or dicecious ; but its delicate 
thallus and the corymbiform arrangement of the receptacles are very 
characteristic. No transitions have been found between the dicecious and 
hermaphrodite condition comparable to those found in the marsh F. cera- 
noides (see p. 343), which certainly would have been found in transitional 
varieties if only a single species were concerned. In spite of individual 
variability, there is no reason to doubt the validity of any of the species 
listed. А 
Tug RELATION OF MARSH SPECIES TO Rock SPECIES. 
It is a tolerably safe axiom to adopt, that all the Fucoids found on salt 
marshes and in analogous associations have been derived primarily, at a 
more or less remote epoch, from rock species. This leads to two general 
questions :— 
(1) Are the marsh and loose-lying Fucoids to be regarded as distinct 
species, or merely as peculiar varieties or forms of the rock species ? 
(2) Which of the rock species is the ancestor of each marsh species ? 
The two questions are interdependent, and will be answered by considering 
each species represented on the marsh in detail. 
The Marsh Forms of Pelvetia. 
PELVETIA CANALICULATA, varr. LIBERA, ©. M. Baker, RADICANS, Foslie, et 
CORALLOIDES, S. M. Baker. 
These striking salt-marsh algæ, one of which (the var. libera) forms an 
undergrowth with Salicornia europea over extensive areas in the Blakeney 
marshes, have already been discussed in some detail by one of us (Baker, 
1912). Their form is not very divergent from typical rock Pelvetia, the 
chief peculiarities being the absence of sexual reproduction, the curling of 
