76 SPOROCHNACE^.— Desmarestia. iv. 



vertically, the innermost of whicli are of largest size, and the cells of eacli row to 

 the cii'cumference of less and less dimensions. The substance of the frond when 

 quite fresh is cartilaginous, but it soon becomes flaccid in the air ; and the colour, 

 which at first is a bright bay, rapidly changes to verdigris green. The fructification 

 is borne on the lowermost divisions of the whorled filaments, and forms moniliform 

 strings of spores springing from the inner faces of the branch. These are deve- 

 loped by the metamorphosis of secund ramuli, and consist of a large number of 

 very minute, oblate spores, which fall asunder when mature. In drying, the plant 

 adheres firmly to paper. 



I am indebted to Mr. Congdon for one of the few specimens of this rare plant, 

 which he succeeded in saving during a very hasty visit to the shore near the 

 mouth of the Cape Fear River. It is roughly dried, and I have, therefore, been 

 obliged to use more carefully preserved (British) specimens to give an idea of the 

 natural appearance of the species (at PI. IV. fig. A \.), but I have drawn the mag- 

 nified figures (2, 3, 4, 5, 6) from Mr. Congdon's specimen, so that there can be no 

 doubt of their identity. The description of the species given above is mostly 

 copied from the Phycologia Britannica. The magnified figures in PL 64 of that 

 work, especially figs. 2 and 4, are much less correct than the corresponding one 

 (2 and 5) now given. 



II. DESMARESTIA, Lamouroux. 



Frond linear, either cylindrical, compressed or flat, pinnated, solid, traversed by 

 a slender articulated filament (or axis) ; the solid parts composed of several rows 

 of small cells. Branches when young producing along the margin, and from the tips, 

 tufts of byssoid, articulated, repeatedly pinnate filaments. Fructification unknown. 



This genus, of which the fruit is at present unknown, is readily distinguished 

 from Arthrocladia, by the structure of the frond. Here there are not the knots 

 along the stem and branches, whorled with delicate filaments, which mark that 

 genus ; and moreover the frond, in the present group, is destitute of a tubular 

 axis of large calibre. It is true that the articulated filament which traverses the 

 stem and branches in Desmarestia may be compared with the articulated tube of 

 Arthrocladia, but the former consists of a string of single cells, placed end to end ; 

 the latter is a compound structure, whose walls and septa are both made up of a 

 great number of cells. 



The manner in which the frond is developed may be readily seen by examining, 

 under the microscope, any tip of a young branch in jjrocess of formation ; par- 

 ticularly in the young points of D. viridis and D. ligidata, in which species the 

 frond is more transparent than in D. aculeata. In D. viridis the young branch is 

 prolonged, at its apex, into a confervold filament, formed of a row of cylindrical 



