gradually becoming smaller and more slender. In the last series,"which 

 are more or less clothed with setaceous simple or forked rainuli, from a 

 quarter inch to upwards of an inch in length, are imbedded one or two 

 elliptical vesicles from one to two lines in diameter. The receptacles ter- 

 minate most of the lesser branches of fertile specimens, and are often 

 much produced : when young, they are clothed with setaceous ramuli, ex- 

 actly as the barren pinnules, but become more or less naked in an advanced 

 state, and at length torulose. They contain numerous conceptacles, of the 

 usual structure. Substance woody in the stem, coriaceous and tough in the 

 branches. Colour a yellowish olive green, becoming black in drying. 



This is the largest and finest of the British Cystoseirce, and 

 Then grown under circumstances favourable to its full deve- 

 opement, it is a very handsome plant. Our figure represents 

 mly the lower part of a stem, and one of the branches. To do 

 full justice to the frond would require a folio plate. 



The principal stem near its base, and some of the lower 

 branches, which are shorter and more simple than the rest, pro- 

 duce numerous simple or forked linear, mid-ribbed leaves, one 

 of which is represented at fig. 2. These are borne nearly in the 

 order of the usual ramuli, but sometimes more densely inserted, 

 and almost fasciculate. 



From C. ericoides, with which only among British species it 

 can be confounded, C. fibrosa may always be known by its more 

 slender branches, the large size of its air-vessels, and the very 

 long, filiform receptacles clothed with setaceous ramuli ; nor does 

 it exhibit, when growing, those brilliant rainbow tints for which 

 C. ericoides is so remarkable. It is by no means so commonly 

 clothed with animal parasites as our other species, but is fre- 

 quently infested with Elachistea fiaccida, a plant which I be- 

 lieve to be peculiar to it. 



Fig. 1. Cystoseira fibrosa. 2. One of the leaves : — bolh of the natural size. 

 3. Keceptad.es and vesicle: — slightly magnified. 



