ZONES OF MARINE VEGETATION. 701 



between the 22d and 26th degrees of latitude. The Gulf-weed has 

 never been found attached, but always floating. In that state it is 

 healthy, pushing out new fronds, but no fructification . has been seen. 

 Harvey conjectures that it may be a pelagic variety of Sargassum vul- 

 gare, in the same way as the variety sub-ecostatus of Pucus vesiculosus 

 has never been found attached, but growing in salt marshes. The 

 Macrocystis pyrifera, and the Laminaria radiata are remarkable for 

 the size and extent of their range. Immense green meadows of the 

 Macrocystis are met with in every latitude. It requires a mean depth 

 of 6 or 9 fathoms. Many specimens have been seen 300 feet long. 

 Hooker estimated some, in a strait between the Orozet Islands, at 

 700 feet. It girds the globe in the southern temperate zone, but not 

 in the tropics nor in the northern hemisphere. The tribe Fucoidese 

 are met with in abundance towards the poles, in which regions they 

 are observed to attain their greatest bulk, diminishing and ceasing as 

 they approach the Equator. Cystoseirese foUow a course in the higher 

 latitudes of the southern hemisphere similar to the Fucoidese. Hooker 

 remarks that throughout aU latitudes the two tribes Fucoidese and 

 ■CystoseiresB form the prevailing marine vegetation, and that the 

 genera of north cool zones are represented by others, in the south. 

 The genera Fucus and Himanthalia, in the north, are represented by 

 D'Urvillsea and Sarcophycus in the south ; so also the genera Cysto- 

 seira and Halidrys of the former are represented by Cystophora and 

 Scytothalia in the latter. Laminarias inhabit the antarctic ocean, and 

 stretch northwards to the Cape of Good Hope. The red, green, and 

 purple Lavers of the British seas are found at the Falkland Islands. 

 Lessonia, with a stem 10 feet long and 12 inches in circumference, 

 and its fronds 2-3 feet long and about 3 inches broad, is found in im- 

 mense masses oflf the Patagonian regions. D'UrviUsea utUis is another 

 large antarctic Seaweed, which, along with Lessonias, is often found 

 at the Falkland Islands, formed by the surf into enormous vegetable 

 cables, several hundred feet long, and thicker than the human body. 

 The stems of Lessonia, when washed ashore, look like dead wood. 

 Of the strictly antarctic marine plants. Hooker has identified l-5th 

 with those of Britain. In the north-west American Sea we meet with 

 the remarkable ISTereocystis, consisting of a very long thread-like stalk 

 bearing a large vesicle and fronds ; while in the Australian and New 

 .Zealand regions we have the peculiar genera of Cystophora, Hormo- 

 sira, Lansburghia, and others. At Vancouver's Island Laminajias occur 

 of large size. Nereocystis Lutkiana has a stipe attaining the length 

 of 300 feet, and Alarise have fronds 20-30 feet long. Georgetown, 

 Tasmania, according to Harvey, is a good locality for Algse — all 

 attaining a large size ; Dasyas 2-3 feet long ; Polysiphonia Hookeri 

 even longer ; Griffithsia setacea and G. corallina, nearly 2 feet long ; 

 CaUithamnions, covering a large sheet of cartridge paper; a single 



