SECT. n. GRIFFITHSIA. 233 



on the branches with two or three branch-like hairs be- 

 neath them, and tetraspores set in the coloured parts 

 of the joints with a thorn between each, for in this plant 

 the centre of the joint is hyaline, the rest coloured. 



The genus Griffithsia contains various species of bright 

 rose-coloured plants, which become bleached when put 

 into freshwater, and form a circle when spread out. Soft, 

 tender, and gelatinous, they form dense tufts of jointed 

 and branched filaments on rocks at low water mark. The 

 filaments are slender below, capillary and forked above, 

 and the joints contain one linear upright rose-coloured 

 tube, which is seen throughout their transparent walls : 

 a distinguished mark of the genus. Tetraspores are 

 borne on the hair-like jointed ramuli, and spores are 

 amassed in coated roundish sessile nuclei, surrounded 

 by minute hair-like fibres. Several species once called 

 Griffithsia differ so much from the others, that they are 

 by some referred to Halurus, which has the stems and 

 branches thickened by overlapping whorls of tiny forked 

 jointed and curved ramuli. They are propagated by 

 spores, enclosed in clusters of nuclei borne on the tips of 

 short branches, with a mass of curved ramuli folding 

 over them, and by tetraspores attached to the inside of 

 another set of curved ramuli. Antheridia have been 

 discovered in several genera of the group Ceramiacese, 

 especially in Ceramium, Callithamnion, Griffithsia, and 

 Halurus. They consist of little clusters of cells variously 

 arranged, in which the active particles known as sperm- 

 atozoids are generated. 



The Polysiphonia are Algae, seen in tufts from ten to 

 twelve inches long, of usually much branched jointed 

 filaments, on rocks, corallines, and the smaller Algae at 

 low water mark. The joints of the filaments contain 

 upright tubes, full of purple or reddish brown matter, 

 which is seen through their transparent walls. The 

 number of these colour tubes vary from four to ten, 



