52 RHODOMELACEiE. 



V. 



branched ; the main stem and branches somewhat angularly bent. All the divi- 

 sions patent, and all the internodes short. Substance rigid. Colour very dark. 

 This variety is readily known by its patent, distichous branches, rigid substance, 

 and internodes uniformly shorter than in the preceding forms, with which it seems 

 to connect the following. 



Var. 6. Durkeei. Stem 2-3 inches high, thicker than hog's bristle, compressed (?), 

 distichously branched, repeatedlj^ pinnate ; the main stem either simple or forked, 

 with several lateral branches. Branches definitely circumscribed, round-topped, 

 bi-tripinnate, the pinnte a line asunder, patent ; pinnules subulate and erect. Arti- 

 culations visible in all parts of the frond, and uniformly much shorter than their 

 diameter. Colour a dark brown. Substance rather rigid. This plant, which I 

 first received from Dr. Durkee of Boston, is so unlike many of the preceding 

 varieties, particularly those called j)lumosa and gracillima, that few persons, on a 

 mere inspection of a solitary specimen, would suspect them to belong to the same 

 species ; and when first I examined Dr. Durkee's specimen I regarded it as speci- 

 fically distinct, and hoped it might be allowed to bear his name. A more extended 

 reference to other specimens from various quarters now induces me to consider it a 

 very extreme form, in wliich the characters of the var. disticha are exaggerated. 



Plate XVII. C. Fig. 1. Polysiphonia nigrescens, var. Durkeei ; the natural size. 

 Fig. 2, part of a branch and ramulus ; jig. 3, cross section of a branch ; both mag- 

 nified. 



2.5. Polysiphonia Woodii; stem robust, flexuous, strongly compressed, distich- 

 ously branched, decompound-pinnate ; pinnae (or primary branches) distant, patent, 

 tri-quadri-piunate, the pinnules pinnato-multifid ; ultimate ramuli subulate, in- 

 curved ; internodes in all parts of the frond very much shorter than their diameter, 

 many striate, with pellucid dissepiments, those of the stem with two ( ! ) axes of 

 radiation ; tetraspores in a single row in the ramuli. 



Hab. On the Pacific Coast, in lat. 38° 12', Lieut. Wood (1846 ). Golden Gate, 

 California, Capt. N. Pike (1851). (v. s. in Herb. Hook, et T. C. D.) 



Frond (in the largest specimen seen by me) about 5 inches long, twice as thick 

 as hog's bristle, compressed, somewhat zigzag, distichously branched ; the branches 

 half an inch asunder, alternate, patent, one to two inches long, nearly equal, de- 

 compound pinnate, their primary piuna3 half an inch long, about three or four 

 times pinnately parted, all tlie lacinite alternate. The ultimate ramuli are subulate, 

 acute, incurved, not a line in length. Every part of the frond is exactly distichous. 

 The internodes are visible throughout with the help of a pocket lens, and are much 

 shorter than their breadth, about ten strife or tubes being visible on a lateral view 

 in the ramuli, and a greater number on the larger branches. All the interspaces 

 are pellucid ; in the stem only are the internodes partially coated with secondary 

 cellules. A transverse section of the stem is a long ellipse, having two axes (or 

 foci) round which the tubes radiate, a structure which I have never seen in anv 



