Fig. 3. HALIDRYS SILIQUOSA. 
Colour. When young, greenish olive ; in age, glossy brown ; when dry, black. 
Suhstance. 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 -jL of an inch wide. 
Air-vessels. Long ; pod-like ; tipped with a point ; marked by obscure lines across ; internally, 
divided into compartments. 
Fructification. Minute seeds (spores') in special receptacles, at the ends of the branches, 
thickening them. 
Habitat. 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. 
Suhstance. Tough, leathery. 
Character of Frond. Shrub-like. Stem cylindrical ; thick ; short ; woody ; beset with slender 
branches. Branches irregularly divided ; closely set with short, thorn-like branchlets, 
incurved like a shoemaker’s awl (awLshaped). Altogether very bushy. Boot, 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 XVI. Fig. 66. 
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