SEA WEEDS 387 



base, pointed at the tip, and are jointed to short projections on the 

 main stem ; and both these and the main stem have very large 

 oval air-vessels. The spore-receptacles are mounted on slender 

 stalks which arise from projections on the branches, and are of 

 a bright yellow colour when mature. This species does not grow 

 so near to high-water mark as do the others. Another species, 

 the Twin-Bladder Wrack (F. vesiculosus Plate VIII.) is abundant 

 everywhere along the coast, and is largely used by agriculturists 

 both as manure and as fodder for cattle. The frond is flat, with a 

 distinct midrib, and a non-serrated edge. Air-vessels are not 

 always present, but when they are they usually occur in pairs, 

 one on each side of the midrib, and are globular in form. The 

 spore-receptacles are situated at the tips of the branches, are full 

 of mucus, and are frequently forked. The last of the common 

 species is the Channelled Wrack (F. canaliculatus Plate VIII.), 

 distinguished by a narrow frond, rounded on one side and chan- 

 nelled on the other. It has no midrib or air-vessels, and the fruit 

 is contained in forked receptacles at the tips of the branches. 

 This is the smallest of the genus, and may be found at all levels 

 between the tide-marks. Stunted specimens may also be seen in 

 situations where they are never submerged, but watered only by 

 the spray of the highest tides. 



The genus Himanthalia provides us with a single species (H. 

 lorea) which is very peculiar on account of the small size of the 

 frond as compared with the enormous di- 

 mensions of the spore-receptacles. The 

 young frond is a pear-shaped sac which 

 soon becomes flattened into a hollow disc. 

 This disc then becomes solid, and concave 

 above, and from its centre there arises a 

 bi-forked, strap-like receptacle that often 

 reaches a length of three or four feet, and 

 may be mistaken for the frond of the 

 weed by those who do not take the trouble p ia 273. Himanthalia 

 to examine it. This weed is commonly lorea 



known as the Sea Thong. 



Belonging to the genus Cystoseira we have a few well-known 

 weeds with conical disc-roots, and shrubby fronds with woody stem 

 and alternate branches. The air-cells are hi the substance of the 

 frond, and the spore- receptacles at the tips of the branches. One of 

 the species (C. ericoides) is of a heath-like habit, with a short, woody 



