Fig. 3. HALIDRYS SILIQUOSA. 



Colour. When young, greenisli olive; in age, glossy brown; when dry, black. 

 Suhstaiice. Tough, leathery. 



Character of Frond, Stem and branches. Everywhere compressed; long and 

 narrow with parallel sides {linear). Branching alternate; repeated. 

 The whole plant at one level, as if cut out of paper. 



Measurement. From 1 to 4 feet long; about -^^ of an inch wide. 



Air-vessels. Long; pod-like; tipped with a point; marked by obscure lines 

 across; internally, divided into compartments. 



Friidifimtion. Minute seeds {spores) in sjoecial receptacles, at the ends of the 

 branches, thickening them. 



Ilahitat. All round the coast. On rocks and in pools, at and below half -tide 

 level; common. 



Fig. 4. CYSTOSEIRA ERICOIDES. 



Colour. When fresh, clear olive; giving out brilliant iridescent tints (blue 

 and green) in the water. When dry, black. 



Snhstance. Tough, leathery. 



Character of Frond. Shrub-like. Stem cylindrical; thick; short; woody; be- 

 set with slender branches. Branches irregularly divided; closely set 

 with short, thorn-like branchlets, incurved like a shoemaker's awl (awl- 

 shaped). Altogether very bushy. Root, a large hard disk. 



Measurement. From 1 to 2 feet long. 



Air-vessels. Inflations in the branches. Very small, solitary, just below the 

 receptacles. 



Fructification. Minute seeds {spores) in special receptacles at the ends of the 

 branches, thickening them. Receptacles, cylindrical; lumpy with 

 tubercles; beset with thorns. 



Habitat. South of England. West and South of Ireland. On rocks near 

 • low-water mark and in tide-pools. 



Often infested by a very minute, tufted, parasitic alga, Elachista pulvinata; 

 for which see Plate XYI. Fig. 66. 



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