30 RHODOMELACE^. v. 



DiGENiA simplex^ Ag. Sp. Alg. 1. p. 388. Digmia Wulfeni, Kiitz. Phyc. Gen. t, 

 50. f. 2. Sp. Alg. p. 841. Confm^va simplex. Wiilf. Fucus Lycopodium, Turn. Hist. t. 

 199. (Tab. XIII. D.) 



Hab. Abundant at Key West, W. H. H. &c. Key Biscayne, Prof. Tuomey, (No. 

 61. 62). 



Fronds 4-8 inches long, as thick as crow's quill, irregularly dichotomous or alter- 

 nately branched ; the branches either simple or bearing near the summit a second 

 series of lesser branches ; sometimes very bushy. The lower parts of the stem 

 are generally bare, but the upper half and all the branches are very densely 

 clothed on all sides with shaggy, setaceous ramuli, from a quarter to half an inch in 

 length. These ramuli are fihform, simple or slightly branched, articulate, the 

 internodes about as long as broad, coated with small cells arranged in many longi- 

 tudinal lines. A cross section of a ramulus shows a central tube with two or 

 more series of radiating cells set round it. I have not found fruit on my speci- 

 mens. Colour when quite fresh a dark brownish red, becoming brown in drying 

 and dirty white after exposure to the sun. Substance very rigid and horny, tough. 

 In drying, the plant does not in the least adhere to paper. 



A very coarse, shaggy plant, apt to be infested with numerous vegetable and 

 animal parasites, particularly corallines. It is very difficult to find specimens 

 free from extraneous growth, or having the ramuli perfect. In our figure the 

 parasites are omitted. 



Plate XIII D. Fig. 1. Digenia simplex, the natural size. Fig. 2. Some ramelli, 

 springing from a fragment of the stem ; Jig. 3, portion of a ramellus ; the two 

 latter figures more or less highly magnified. 



VIII. POLYSIPHONIA. Grev. 



Frond filiform, rarely sub-compressed, articulate (at least the younger parts, the 

 older having an articulate axis) ; internodes of the stem (or axis) composed of nu- 

 merous, tubular, elongated cells of equal length, radiating round a central cell, and 

 generally containing endochrome. Conceptacles ovate or urceolate, containing a tuft 

 of pearshaped spores. Tetraspores imbedded in the distorted, ultimate ramuli. 



An immense genus inhabiting all regions from the Polar basin to the equator ; 

 very variable in size and external habit— some species being two to three feet in 



