SEA WEEDS 371 



on account of its peppery taste. It is found in the tide pools on 

 many parts of the coast, and varies much in size, form, and colour 

 according to the situation in which it grows. The plants which are 

 exposed to the air at low tide are usually small, and of a pale brown 

 colour, while those found in the permanent rock pools at or near 

 low-water mark are larger and dark brown or purple. The fronds 

 are flat and cartilaginous, with stout branches bearing alternate 

 divided branchlets, which are blunt at the tips. The stem itself 

 is unbranched. The spores are pear-shaped, in oval cells ; and 

 the tetraspores are irregularly distributed near the tips of the 

 branches. 



Another common species, known as the Tufted Laurencia 

 (L. cfespitosa), is very similar to the last mentioned, and is not 

 easily distinguished from it. It is, however, of a bushy habit, while 



FIG. 254. Laurencia plnnatifida FIG. 255. Laurencia obtusa 



L.pinnatifida is flat, and its fronds are less firm. This species 

 grows on rocks and stones between the tide-marks, and is varie- 

 gated in colour from a pale green to a purple. 



A third species the Obtuse Laurencia (L. obtusa) is widely 

 distributed on our coasts, and may be known by its thread-like 

 bipinnate fronds with short blunt branchlets, cup-shaped at the tips. 

 It is parasitic on various other weeds. 



The genus Lomentaria includes a few weeds with tubular fronds 

 that are constricted at intervals, and divided internally by trans- 

 verse membranous septa. The spores are pear-shaped and lodged 

 hi spherical cells ; and the tetraspores are scattered on the surface 

 of the branches. One species called the salt-wort (L. Ttaliformis) is 

 widely distributed. Its colour is pink, sometimes yellowish, and it 

 grows on rocks or stones, and sometimes on other weeds. It may 

 always be known by its spherical fruit, without any visible opening, 



