250 ALG^E. 



attention, and the result of his labours is displayed in one of 

 the most beautiful and useful books connected with this branch 

 of natural history, the Algce JBritannicce, Inarticulate. His ar- 

 rangement and characters of the genera of that division of the 

 Algai I have almost implicitly followed, as the best that has ap- 

 peared. The Diatomea he lias kindly undertaken expressly for 

 this work. I am indebted to W. H. Harvey, Esq. of Summer- 

 ville, near Limerick, for all that concerns the rest of the Alga; 

 and I am here anxious to express my great obligations to that 

 gentleman for the readiness with which, at my request, he under- 

 took this most difficult task, and for which his zeal and his know- 

 ledge have rendered him peculiarly qualified. Those who have 

 occasion to study the British species of this extensive tribe of 

 plants, will, I am sure, duly appreciate his labours. The public, 

 too, as well as myself, are greatly indebted to the late Capt. 

 Carmichael of Appin, Argyleshire, for the ardour with which 

 he explored the coasts in the vicinity of his residence, and the 

 number of previously undescribed species which he has added 

 to the catalogue. Upon his death, his herbarium and MSS. 

 and drawings came into my possession, and no one is more 

 anxious to do justice to the memory of this eminent crypto- 

 gamist, by recording his discoveries, than are Mr. Harvey and 

 myself. 



Synopsis of the Genera. 



Div. I. INARTICULATE. 



Plants foliaceous, spreading or filiform , inarticulate (or rarely and 

 only apparently articulated'). 



Tribe I. Fucoideje. Marine plants, of an olive-brown or 

 olive-green colour, becoming black on exposure to the air; of a 

 firm, coriaceous or ligneous substance and fibrous texture, tear- 

 ing with facility in a longitudinal direction. Frond ivith a hard, 

 scutate root, furnished in many species ivith distinct leaves. 

 Vesicles or air-vessels generally present, which are either uniform 

 dilatations of particular parts, or distinct bodies supported on 

 little stalhs. Fructification ; tubercles contained in distinct recep- 

 tacles, or imbedded in the frond and containing dark-coloured 

 seeds surrounded ivith a pellucid llmbus, which escape by a ter- 

 minal pore. Grev. 



1. Sargassum. Frond leaved. Leaves stalked, with a mid- 

 rib. Air-vessels simple, axillary, stalked. Receptacles small, 

 linear, tuberculated (mostly in axillary clusters or racemes). 

 Seeds in distinct cells. Grev. 



2. Cystoseira. Frond furnished with branch-like leaves, 

 becoming more filiform upwards. Air-vessels simple, arranged 

 consecutivelv within the substance of the branch-like leaves. 



