(20) 



of SO doing. The lateral fructification and more membranous substance 

 are characters which will seldom fail to distinguish the species ; but we 

 are not certain whether fresh water and exposure to the action of the 

 air may not have much influence in changing the character of the species, 

 at least as far as the substance of the frond is concerned : that founded 

 on the fructification certainly seems at least to be of more importance. 



Should this form, however, be considered deserving to retain its ground 

 as a species, we are strongly inclined to think that F. Balticus would rank 

 better with the present than with F. vesiculosus, as its substance, in its 

 more perfectly developed forms, is very much the same, as are also 

 to some extent the influences to which the two forms are subjected, and 

 which are so peculiar that they cannot fail in having considerable power 

 in altering the form of the species. Other species also seem to suff'er 

 similar changes from the same cause. A variety of Rhodyraenia j>(il'>nata 

 we have found in brackish water, of large size, and having fronds soft and 

 semitransparent, and much corrugated on the surface. 



Fucus ceranoides, although not so common as F. vesiadosus, is by no 

 means a rare species, being always found in estuaries, and where fresh- 

 water streams mix with the sea, and occasionally in little muddy bays 

 whei*e it is long left by the tide ; this is no reason, however, why the 

 species should be retained, but rather the reverse ; careful observation 

 alone can decide the matter. 



EXPLANATION OP PLATE CXXXVII. 



Fig. 1. — Fucus ceranoides, natural size. 

 2. — Branchlet with receptacle. 

 3. — Section of same. 

 4. — Section of conceptacle. 

 5. — Spores and filaments. All magnified. 



