IV. LAMINARIACE.E.— Chorda. 97 



reniform, undivided, pierced in all parts with roundish holes. Fructification^ cloud- 

 like patches of spores, imbedded in the thickened surface of some part of the per- 

 forated leaf-lobes. 



This genus is very nearly related to the preceding, from which it differs in having 

 a branching stipe, round which a perforated lamina, partially divided into definite 

 leaves, is spirally coiled. There is but one species yet known, viz : — 



Thalassiophyllum Clathrus, Post, and Rupr. lUustr. t. 18, and t. 19. /. Ag. 

 Sp. Alg. 1, p. 139. Kiitz. Sp. Alg. p. 581. Fucus clathrus, Grev. Hist. Fuc. t. 33. 



Hab. On the shores of Russian America, (v. s. in Herb. T. C. D.) 



My specimens of this are so imperfect, that I prefer copying the following 

 account given by Dr. H. Mertens of its appearance in a living state : — 



" The ocean hardly boasts a more beautiful production than this ; it is generally 

 about the height of a man, very bushy and branched, each branch bearing a broad 

 leaf at its extremity, which unfolds spirally, and by this gradual development pro- 

 duces the stipes with its branches and lateral divisions. A spiral border, wound 

 round the stipes, indicates the growth of the frond. The fi'ond presents a large, 

 convex, bent lamina, without nerves ; or to a certain degree a leaf, of which one 

 half is wanting, for the stipes may be considered as an excentric nerve. A number 

 of rather long, narrow perforations, arranged in a radiate form, give the frond the 

 appearance of a cut fan ; these foramina being coeval with the formation of the 

 frond, and apparently not owing to inequalities of substance. At first, these fora- 

 mina, which are situated near the stipes, and Avhere the frond is bent in, are round, 

 and have their margins turned outwards ; but by the subsequent growth of the 

 frond they become longer, and their margins disappear ; in the middle of the frond 

 they are like true clefts, but nearer the margins, from the greater development of 

 the leafy substance, they are more contracted in their breadth and therefore seem 

 round. The frond has a complete and entire margin, but is frequently torn ; its 

 substance is coriaceous. I have never detected any fructification. The root resem- 

 bles that of the larger Laminarias, but is more woody. This fucus is very plentiful 

 in the bay of Illuluk, and round the whole island of Amaknak. It clothes the rocky 

 shore, like a thick hedge, for a space of 60 or 80 feet, forming, at a little distance, 

 a very pleasing feature in the scenery." H. Mert. in Hook. Bot. Misc. 3, p. 5, 6. 



IX. CHORDA, Stack. 



Root scutate. Frond simple, cylindrical, tubular ; its cavity divided by transverse 

 membranes into separate chambers. Fructification a stratum of obconical spores, 

 covering the whole external surface of the frond. 



VOL. m. ART. 4. • o 



