FIRST DIVISION OP PLANTS. 



189 



species which grow at the bottom of the ocean, 

 may have some resemblance to those of the polar 

 circle. On the shores of the British islands, it 

 is easy to perceive that certain species become 

 more plentiful and luxuriant as we travel from 

 north to south; and on the other hand, that 

 several others occur more frequently, and in a 

 finer state, as we approach the north ; while 

 others again possess too extended a range to be 

 influenced by any change of temperature between 

 the northern boundary of Scotland and the 

 south-western point of England. The researches 

 and observations of Lamouroux have demon- 

 strated satisfactorily that the great groups of 

 algae do affect particular temperatures or zones 

 of latitude, though some genera may be termed 

 cosmopolite. Thus the genus codium, a, small 

 greenish coloured arid branched algoe, and the 

 family Ulvaceae, which consist of extremely 

 thin, transparent, and purplish membranes, are 

 scattered over every part of the world. Codium 

 tomentoswm is found in the Atlantic, from the 

 shores of England and Scotland to the Cape of 

 Good Hope in the Pacific; from Nootka Sound 

 to the southern coast of New Holland. It abounds 

 in the Mediterranean, on the shores of France, 

 Spain, and Africa, and is common in the Adri- 

 atic; more recently it has also been brought from 

 the coasts of Chili and Peru. This plant, how- 

 ever, is not a social one, to make use of a term 

 that Humboldt has applied to some phoenogam- 

 ous plants. It grows even in the same locality, 

 in a solitary and scattered manner. The ulvacece, 

 on the contrary, are strictly social, and preserve 

 this character in every part of the world. They 

 appear, however, to attain the greatest perfection 

 in the polar and temperate zones. That they 

 are capable of sustaining very intense cold, is 

 proved by the fact that five specimens of them 

 were picked up in high latitudes of the Arctic 

 ocean, by some of the gentlemen in Captain 

 Parry's voyages. The JFucoidece, comprehend- 

 ing the sea tangles, increase as we leave the polar 

 zone, especially in the variety of species. But 

 the natural groups into which they are separated, 

 are strongly marked in their distribution. The 

 fuci flourish between the latitudes 65° and 44°; 

 and according to Lamouroux, are rarely seen 

 nearer to the equator than 36°. In New Hol- 

 land, remarkable alike for its vegetable and ani- 

 mal productions, a distinct group of cystoseirce 

 predominates, as remarkable in the water as the 

 aphyllous acacice are on land. Their stems are 

 compressed, often appearing jointed: the branches 

 spring from the flat side and not from the angles. 

 The Red sea is full of another family, sargassa, 

 of which several species, consisting of small 

 branched and dark olive green plants, are 

 common on our British shores. It is principally 

 to one or two species of this family that the 

 popular name of gulf weed is applied by marin- 



ers. The prodigious accumulations of these 

 plants were first encountered by the early Por- 

 tuguese navigators. Columbus compares them 

 to extensive inundated meadows, and states, 

 that they absolutely retarded the progi-ess of his 

 vessels, and threw the sailors into consternation. 

 Such accumulations occur on each side of the 

 equator, in the Atlantic, Pacific, and Indian 

 oceans; but the sea particularly denominated 

 Mer do Sargasso, by the Portuguese, stretches 

 between the 18th and 22d parallels of north lati- 

 tude, and the 25th and 40th meridians of west 

 longitude. Humboldt describes the two banks 

 of sea weed that occur in the great basin of the 

 northern Atlantic ocean. "The most extensive 

 is a little west of the meridian of Fayal, one of 

 the Azores, between latitude 25° and 36°. Vessels 

 returning to Europe, either from Monte Video 

 or the Cape of Good Hope, cross the bank nearly 

 at an equal distance from the Antilles and Can- 

 aries. The other occupies a much smaller space, 

 between 22° and 26°, eighty leagues west of the 

 meridian of the Bahama islands. It is generally 

 traversed by vessels on the passage from the 

 Caicos to the Bermudas." That these plants are 

 produced within the tropics, there can hardly 

 be a question; but at what depth they vegetate 

 is still involved in obscurity. Neither is it 

 clearly ascertained why the banks of weed should 

 always occur in the same places. The supposi- 

 tion that they proceed with the gulf stream, 

 from the gulf of Mexico, whence the name of 

 gulf weed, is now exploded. It is evident that 

 the gulf stream would convey them rather to 

 the banks of Newfoundland than to the latitudes 

 in which they usually occur; and it could not, 

 in any case, accumulate them to the south of 

 the Azores. 



Some of the algae prefer the southern sides 

 of rocks; others affect an eastern, western, or 

 northern exposure; but they change their posi- 

 tion according to the difference of latitude, those 

 which are found on the southern side, in cold 

 climates, being generally seen on the northern 

 in the warmer and temperate regions. Certain 

 species live near the surface, and close to the 

 sea beach; others at various degrees of depth. 

 The first would seem to enjoy the regular ex- 

 posure to light and heat which they experience 

 during the turnings of tbe tide: the second, on 

 the contrary, show the influence of the atmos- 

 phere; and growing and fructifying in depths 

 where the light can scarcely ever penetrate, they 

 bear, without receiving any injury, botli the enor- 

 mous column of water which constantly presses 

 upon them, and the severe cold which exists In 

 those regions. There are even parasitical algse 

 which grow indifferently upon all the others, and 

 some which only affect peculiar species. Many 

 sea weeds prefer such spots as are exposed to the 

 fury of the waves, and the action of the current. 



