212 CERAMIACEiE. v. 



always longest in the older parts of the frond. The nodes are universally swollen, 

 thicker than the internode above and below, each internode sitting in the one below 

 it as in a little cup. In the young state each node is crowned with a whorl of 

 minute spine-like processes, which are gradually obliterated in age, and are only to 

 be found, in old plants, on the youngest branches. Young plants are also covered 

 with copious, very slender hairs, afterwards deciduous. Favellce subtended by 

 three or four small branchlets. Tetraspores rather prominent, whorled round the 

 nodes of the lateral ramuli. Colour a dark purple, passing into brick-dust-red in 

 fresh water. Substance rigid and harsh. It does not adhere to paper in drying. 



Plate XXXIII. C. Fig. 1. A tuft of Centroceras clavulatum, the natural size. 

 Figs. 2 and 3, portions of filaments of different ages ; Jig. 4, apex of a branch ; Jig. 

 5, internodes of the stem ; all more or less magnified. 



III. CERAMIUM. Lyngb. 



Frond filiform, dichotomous or somewhat pinnate, articulate ; the articulations 

 either partially or wholly coated by small cells not arranged in lineal series. 

 Favellce sessile on the branches, subtended by a few involucral ramuli, and contain- 

 ing, within a hyaline periderm, many angular spores. Tetraspores formed by a 

 transformation of some of the cortical cells, more or less projecting from the 

 surface, roundish, triangularly divided. 



The fronds generally grow in dense tufts, seldom exceeding six inches in height, 

 and often not half that measurement. The stems vary in diameter from the thick- 

 ness of a hog's bristle, or rather more, to the fineness of a cobweb. Some species 

 are so completely corticated with minute coloured cellules as to be nearly opaque ; 

 others are beautifully variegated with hyaline and coloured bands alternately 

 placed ; the coloured or corticated portion of each cell being that nearest to the 

 node, the hyaline band occupying the central region of the internode. Many of 

 the species, perhaps all, are, when young, clothed at the nodes with very fine, soft, 

 hyaline hairs, which, as the frond advances in age, fall away, leaving the articula- 

 tion quite smooth. Other species are armed at the nodes with thorn-like processes 

 or prickles, but none of this section have yet been found in North America. 



The number of ioo^-species has befen largely increased of late years, partly by 

 the discovery of new forms, and partly by splitting into several the specific ideas 

 (so to say) of the older botanists. Some of these newly proposed species are no 

 doubt proper to be retained, but I fear the splitting process has been carried far be- 

 yond its legitimate limits. The North American species naturally divide into two 

 sections, in the first of which the cortical cells cover over either the whole of the 



