362 TEE SEA SHORE 



with coinb-like branchlets, growing on the stems and fronds of 

 other weeds found on our northern shores. The other (P. elegana), 

 with narrower fronds, in long flaccid tufts, is found all round 

 our coasts. 



Our last genus of the Ceramiacece is the large and typical one 

 Ceramium, which contains about a dozen British species in which 

 the frond is threadlike, jointed, branched or forked repeatedly, with 

 the tips of the branchlets usually curled. The spore-clusters are 

 enclosed in transparent sessile sacs, surrounded by a whorl of very 

 short branchlets ; and the tetraspores are embedded in the cortex, but 

 distinctly visible. As a rule the fronds are very symmetrical, and 

 the branches radiate in a regular fan-like manner. 



In one species of the genus the frond is completely covered with 

 cortex cells, and at each node of the frond there is a single spine 

 which, although so small as to be invisible without a lens, so effec- 

 tually locks the threads together that they form an entangled mass 

 that is not easily arranged to the satisfaction of the collector. The 

 species referred to is C. flabelligemm the Fan-bearing Ceramium 

 and is very rare except in the Channel Islands. 



Other species are armed with one or more spines at the nodes, 

 but the nodes only are covered with cortex cells, which render them 

 opaque, while the internodes or joints are transparent. In this 

 group we have C. ciliatum the Hairy Ceramium, with reddish- 

 purple segments, and a regular whorl of hairs, directed upwards, 

 round each node ; each hair or spine consists of three segments. 

 This plant is common during the summer and autumn, and may be 

 found in the tide pools at all levels, either attached to the rocks or 

 parasitic on other weeds. The same section contains C. echinotum, 

 with rigid, forked fronds, and irregularly- scattered one-jointed 

 spines ; it is common on the south coast, where it may be found on 

 the rocks and weeds of the upper tide pools ; and 0. acanthonotum, 

 also common in the rock pools, with a single strong three- jointed 

 spine on the outer side of each filament. The last-named weed is 

 found principally on the northern shores, especially on rocks covered 

 with the fry of the common mussel. 



Other species are characterised by transparent internodes as 

 above described, but have no spines at the joints, and may thus be 

 easily floated on to a sheet of paper without the troublesome matting 

 of their fronds. These include the Straight Ceramium (C.strictuni), 

 with erect and straight branches growing in dense tufts, and con- 

 spicuous tetraspores arranged round the nodes of the upper branchlets, 



