160 NTOP8IS OF BRITISH ST. A WEEDS. 



Uab. West of Ireland. On turf-banks at extreme high-water 



mark. 

 Codium amphibium was discovered by Mr. fct 'Calla, in 

 October 1843, spreading in patches of greal extent along 

 the edge of the sea, over the surface ot a turf-bog which 



meets the sh<>re at Ronmlstone Hay. In this situation the 

 plant is exposed alternately to the influence of salt ami of 

 fresh water, and, it would appear, is even affected by at- 

 mospheric changes: for its discoverer has observed that 

 " in dry weather it loses all its characters, the frond shrink- 

 ing to a mere nothing, but on the return of moisture it 

 immediately gets fresh again." 

 283. tomentosum ( The tomentose Codium) ; frond linear, dichoto- 



mous, cylindrical or compressed, Ag. Sp. Alg. v. l.jp. 452, 



(Atlas, PL LXI. Fig. 285.) 

 Codium elongatum, Ag. C. lineare ? Ag. C. filiforme ? Monig. 



Spongodium tomentosum, Lamour. S. commune, Bory. 



Fucus tomentosus, Huds. Agardhia dichotoma, areolata, et 



ramentacea, Cabrera. 

 Hah. On rocks in the sea, within the range of the tide ; generally 



near low-water mark. Perennial. Summer. 

 There are slight points of difference, on which authors 

 have founded species, which I cannot but regard as mere 

 varieties of a common type. Such is the C. elongatum of 

 Agardh, a figure of which is given in the * History of 

 Algiers,' published under the auspices of the French 

 Government. This form, which accompanies the common 

 C. tomentosum on the west coast of Ireland, is chiefly re- 

 markable for a great dilatation of the frond immediately 

 under the forking of the branches. This enlargement how- 

 ever may be found in various degrees of development, 

 connecting the most dissimilar-looking individuals of C. 

 elongatum, with the common dichotomous, filiform C. 

 tomentosum. Were C. elongatum admitted as a species, 

 several other forms might be ennobled on grounds as valid. 

 C. tomentosum has to the naked eye quite the appearance, 

 though not the substance or structure, of a sponge ; and 

 indeed very closely resembles in form and colour the 

 Spongia hispida, Mont., offering a beautiful instance of 

 analogy between organisms whose affinity is widely sepa- 

 rated. It occurs throughout the Pacific Ocean, from the 

 shores of Arctic America and Asia to the southern ex- 

 tremity of America ; and is equally dispersed throughout 

 the Atlantic. 



