Plate XXIII. 



Fig. 99. ODONTHALTA 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 alter- 

 nate; 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 

 {pinnatifid). 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 (tetra- 

 spores), contained in lanceolate pods (sticliidid). Scattered along the margins 

 on slender stalks which are either simple or branched. 



Sahitat. Scotland. North of England and Ireland. In pools and on rocks in the 

 sea. Frequent. 



When once seen, this plant cannot be mistaken for any other; and even a 

 study of the figure will make it easy to recognize. It was for a long time sup- 

 posed 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, Stichidium, 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. 



Suhstance. Robust 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 branchlets. 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. 1. 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 Lami- 

 naria digit ata. Common. 



For another Bhodomela, see Plate XXIV. Fig. 103. 



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