14 SARGASSUM. 



most valuable of marine plants. Besides the use made of 

 their decayed fronds for manure, kelp is abundantly procured 

 from their ashes. They are the chief source of iodine ; man- 

 nite may be prepared in considerable quantity from many ; 

 and several afford a grateful winter pasturage to the herds of 

 cattle along the inclement shores of northern Europe. 



SYNOPSIS OF THE BRITISH GENERA. 



* Air-vessels stalked. 



I. SARGASSUM. Branches bearing ribbed leaves. Air- 



vessels simple. [Plate ], A.] 



II. HALIDRYS. Frond linear, pinnate, leafless. Air-ves- 



sels divided into several cells by transverse partitions. 

 [Plate 1, C.] 



** Air-vessels immersed in the substance of the frond, or none. 



III. CYSTOSEIRA. Root scutate. Frond much branched, 

 bushy. Receptacles cellular. [Plate 1, B.] 



IV. PYCNOPHYCUS. Root branching. Frond cylindrical. 

 Receptacles cellular. [Plate 2, A.] 



V. Fucus. Root scutate. Frond dichotomous. Recep- 



tacles filled with mucus, traversed by jointed threads. 

 [Plate 1, D.] 



VI. HIMANTHALIA. Root scutate. Frond cup-shaped. 

 Receptacles (frond-like) very long, strap-shaped, di- 

 chotomously branched. [Plate 2, B.] 



I. SARGASSUM. Ag. [Plate 1, A.] 



Frond furnished with distinct, stalked, nerved leaves, and 

 simple, axillary, stalked air-vessels. Receptacles small, li- 

 near, tuberculated, mostly in axillary clusters, cellular, 

 pierced by numerous pores, which communicate with im- 

 mersed spherical conceptacles, containing parietal spores and 

 tufted antheridia. Name, altered from sargazo, the Spanish 

 term for the masses of floating seaweed common in some 

 latitudes. 



