SECT. ii. LAURENCIACEJ2. 241 



exposure, and like many other florid Algse they lose 

 their colour in fresh water. They are amongst our com- 

 monest sea weeds. The Laurencia pinnatifida is the 

 pepper dulse of Scotland, and is also native on the east- 

 ern and western coasts of North America. Species have 

 been found at the Cape of Good Hope, Australia, and 

 New Zealand. The fructification in this section is quite 

 peculiar. They have tetraspores lodged in the branch- 

 lets ; and egg-shaped conceptacles with a terminal pore, 

 enclosing nuclei with pear-shaped spores radiating from 

 a fibro-cellular mass at their base. The antheridia, 

 which differ in the different species, attain a greater 

 degree of complication than in other tribes. In Lau- 

 reiicia tenuissima they form curious lateral twisted plates 

 of a greyish tint, bordered with large cells. The plate 

 is occupied by the productive cells of a much smaller 

 size, evidently springing from a cellular branched axis. 

 In Laurencia pinnatifida instead of a plate there is a 

 somewhat hollow cup-shaped disc, formed of dart-like 

 vertical groups of pale cells surmounted by two or 

 three larger oily-looking sacs filled with yellow pig- 

 ment. These bodies are sometimes forked, and appear 

 to shoot out from the mass. L. dasyphylla presents a 

 third modification, the antheridium being a sac, and 

 the dart-like groups of cells being ejected from the mi- 

 nute terminal orifice. The moving particles produced 

 in the cells of these three forms, differ a little in shape, 

 and as they do not germinate they are believed to be 

 spermatozoids, though no cilia have been found on them. 



The Ehodomelacese, the last and highest family of 

 florid Algse, are, as the name implies, of a rich red brown 

 colour. None of the other Rhodosperms can vie with 

 them in peculiarity or variety of structure. The fronds 

 may be areolate or reticulate, filiform or variously leafy, 

 articulate or inarticulate. 



Some genera, as for example Dasya, have slender, 

 VOL. i. B- 



