Plate XXIII. 
Fig. 99. ODONTHALIA DENTATA. 
Colour. Deep ruby-red, when growing ; soon turning darker when thrown ashore ; when dried, 
black, except very young plants, or the new shoots of old ones, which retain a 
reddish-pink hue. 
Substance. Membranaceous, but firm and elastic. 
Character of Frond. Flat ; narrow ; obscurely midribbed ; branched. Branching alternate ; 
irregular. Main stem simple or forked ; deeply toothed on each side. Branches 
issuing from the axils of the teeth ; narrow at the base, widening upwards ; either 
toothed or deeply cut into narrow branchlet-like segments {jpinnatifid). The whole 
frond preserving nearly the same width throughout ; and at one level, as if cut out 
of paper. 
Measurement. From 3 to 12 inches long. 
Fructification. Of two kinds ; external. 1. Clusters of seeds (spores)*' contained in ovate, 
transparent cases (capsules). 2. Seeds divided into four parts (tetraspores), contained 
in lanceolate pods (stichidia). Scattered along the margins on slender stalks which 
are either simple or branched. 
Habitat. Scotland. North of England and Ireland. In pools and on rocks in the sea. 
Frequent. 
When once seen, this plant cannot he mistaken for any other ; and even a study of the 
figure will make it easy to recognize. It was for a long time supposed to have its southern 
limit in the county of Durham ; but it has since been found abundantly in a deep pool in 
Gristhorpe Bay, between Scarborough and Filey ; is common at Filey, and has been picked 
up as low as Flamborough Head. It is magnificent in size at the Giant’s Causeway in Ireland. 
* N.B. For brevity’s sake the reader is requested to accept this explanation of the words 
Spore, Tetraspore, Capsule, Stichidiimi, as here given once for all. The terms will be used 
hereafter as a matter of course. 
Fig. 100. RHODOMELA LYCOPODIOIDES. 
Colour. A dark-brownish red ; becoming darker in drying. 
Substance. Eobust and elastic ; young branches soft ; old ones harsh. 
Character of Frond. Thread-like (filamentous) ; tufted ; branched ; the filaments opaque. 
Stems long, thread-shaped (filiform), simple ; or divided near the base into several 
long, simple branches ; densely clothed with slender, feathery, finely-divided branch- 
lets. These dying partially down in winter, the stems are left bristling with their 
stunted remains ; in which condition the plant can hardly be recognized ; and in the 
second summer, when it has thrown out fresh branchlets, the old and new growths 
are found together. 
Measurement. From 4 to 18 inches long. 
Fructification. Of two kinds; chiefly external. I. Clustered spores in ovate capsules; 
external. 2. Tetraspores in stichidia, or in swollen branchlets. 
Habitat. Scotland, and the North of England and Ireland. On the stems of Laminaria digi- 
tata. Common. 
For another Rhodomela, see Plate XXIV. Fig. 103. 
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