226 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



different as to seem to indicate totally distinct species. They 

 are indifferently Algre of tlie northern and sovithern hemi- 

 spheres; and some species, as Dichloria viridis and Desma- 

 restia ligulata, are found in both. Of onr British species, 

 Arthrocladia villosa extends as high as Scotland, but 

 Sporochnus 2^eduncidatus and Carponiitra Cahrercc, a 

 very rare if a true inhabitant of our seas, are southern 

 plants. 



210. They form two evident gi-oups distinguished by the 

 freedom or compactness of the fruit-bearing threads. The 

 antennse-form threads of spores in Arthrocladia are very 

 beautiful. In Desmarestia the fruit at present is unknown, 

 though some of the species are extremely common. In the 

 broader forms of D. ligulata, the fronds are distinctly nerved, 

 and sometimes resemble leaves, in consequence of the se- 

 condary nerves, as in that found at Loch Smlly. CJinoo- 

 spora, which is essentially tropical, is remarkable for its dicho- 

 tomous fronds. None of the species of the second group have 

 at present been found in America; but dredging may yet 

 detect individuals which have hitherto escaped notice. Few 

 Algee are more beautiful than Sporochnus pedunculcdiis, 

 when the pear-shaped fructifying branches are terminated by 

 their tufts of threads. The mitreeform receptacles of Carpomi- 

 tra Cahrerce, situated at the tips of the branches, give a sin- 

 gular appearance to the frond, from the peculiar way in which 

 they are seated. Arthrocladia villosa, when placed upon 

 paper, makes it transparent as if dipped in oil,* and Desma- 

 restia ligidata and herhacea have the same property, 



6. FucACE^, Ag. 



Inarticulate ; spores contained in elliptic or spherical con- 

 ceptacles, sunk in the frond. Impregnation by spermato- 

 zoids. 



211. We now come to one of the most important tribes of 

 seaweeds, which seem in many respects to deserve the high 



* It was in consequence of this property, that I named the genus 

 Arthrocladia, Elaiotuma. The name Arthrocladia was proposed two or 

 three months previously by M. Duby. 



