7IO 



NATURE 



\pct. 31, 1878 



observed that the specimens iovixA floating '\a. all the seas are 

 always barren. The question then arises, how is the floating 

 weed propagated ? To this question Dr. Harvey ^ replies : — 

 ' ' It seems to me that the old frond, which is exceedingly 

 brittle, is broken by accident, and the branches, continuing to 

 live, push out young shoots from all sides. Many minute pieces 

 that I have examined were as vigorous as those of a large size ; 

 but they were certainly not seedlings, and appeared to me to be 

 broken branches, all having a piece of the old frond from which 

 the young shoots spring. As the plant increases in size it takes 

 something of a globular form, from the branches issuing in all 

 directions, as from a centre." ^ The specimens brought to this 

 country are merely the uppermost branches, the whole plant 

 often attaining a diameter of three or four feet. The upper 

 branches are of a light olive colour, the lower more or less 

 brown ; the lowest parts of all wither and- decay, and finally 

 drop away. 



With regard to the origin 'of the plant there has 'been much 

 controversy among algologists. On this point Harvey ob- 

 serves: — *" Nothing has yet been discovered; for, though 

 species of Sargassum abound along the shores of tropical coun- 

 tries, none exactly corresponds with S. bacciferum. That the 

 ancestors of the present banks have migrated from some fixed 

 station is probable, but further than probability we can say 

 nothing." Prof. Agardh, however, thought he had found the 

 parent stock in a plant which grows on the banks of Newfound- 

 land ; and in his " Species, Genera, et Ordines Algarum," 

 vol. i., published in 1848 — a year before the second edition of 

 Harvey's "Manual" appeared — thus writes of it: — "Natans 

 semper sterilis, nee in pratis Atlanticis fructigera, Fructiferam 

 et affixam e mari Americanum alluente habeo." In his 

 before-mentioned notes on the alga; collected by the 

 yosephine expedition, after referring to the passage just quoted, 

 he says: — "I have received from the banks in the neigh- 

 bourhood of Newfoundland specimens with root and fruit, 

 which, although somewhat different in form, I nevertheless did 

 not scruple to consider as belonging to the same species " {S. 

 bacciferum) ; and he adds that "from no facts yet come to my 

 knowledge have I had reason to change the opinion I had ex- 

 pressed in 1840 at the meeting of naturalists at Copenhagen, 

 that the floating form originates from the Banks of Newfound- 

 land, and perhaps grows on similar localities on the east coast of 

 America, when it is provided with root and fniit." Since the 

 publication of these observations, additional information relative 

 to the fruit of 6". bacciferum has been obtained. Specimens 

 " covered with fructification " have been found by Mr. Moseley,* 

 the naturalist of the Challenger expedition, in Harrington Sound, 

 Bermudas, which islands lie in the very heart of the Sargasso 

 Sea. 



The fact, therefor*, that S. bacciferum bears fruit when at- 

 tached to the land in the Sargasso Sea and the Gulf Stream, may 

 be considered as established. 



With regard to the comparative antiquity of the Bermudas 

 and Newfoundland plants, it must be observed that they both 

 occur within the influence of the Gulf Stream. It is not likely 

 that the Sargassum could make its way from the northern 

 locality against the current of the stream ; hence it seems most 

 probable that it vegetated first at Bermudas, and thence emi- 

 grated, with the stream, northwards. 



Other facts in connection with the two islands favour this 

 view. Sir Wyville Thomson says^ : — " Bermudas is practically 

 an 'atoll,' or annular coral reef. .... What the basis on 

 which the Bermudas reef rests may be, we have no means of 

 telling ; in fact, its having the form of an atoll precludes the 

 possibility of our doing so. There seems to be little doubt, 

 from Darwin's beautiful generalisation, which has been fully 

 indorsed by Dana and other competent observers, that the atoll 

 form is due to the entire disappearance by subsidence of the 

 island round which the reef was originally formed. The ab- 

 ruptness and isolation of this peak, which runs up to a solitary 

 cone about equal to that of Mont Blanc, is certainly unusual ; 



' "Manual of British Marine Algae," second edition. 



2 The floating gulf -weed is not the only plant which can maintain life in 

 vigour, and propagate itself without producing fruit. Gigartina Teedii, and 

 Griffithsia secutidiflora, have vegeta ed many years on rocks in the vicinity 

 of Plymouth, without producing fruit. They are both natives of the 

 Mediterranean, where they yield fruit freely. 



3 " Manual," /. c. 



■* See extract from Mr. Moseley's letters communicated by Dr. Hooker, 

 Linnean Society's Journal, vol. xiv. It is much to be regretted that Mr. 

 Moseley has sent home no specimens of the Bermudas plant. 



5 " Letters from the Challenger" in Good Words for February, 1876, pp. 



probably the most reasonable hypothesis may be that the kernel 

 is a volcanic mountain comparable in character with Pico in the 

 Azores or the Peak of Teneriffe." It has been also stated ^ that 

 "in the process of excavations carried out in order to accommo- 

 date the great floating dock, a bed of peat, with stumps of cedar 

 trees in a vertical position, was found at a depth of forty-five 

 feet below low-water mark, covered by beds of rock. Most 

 conclusive proof is thus afforded that the Bermudas have changed 

 their level, and sunk since they have been covered with a similar 

 vegetation to their present one. " These statements afford con- 

 siderable evidence of the antiquity of the Bermudas. Now as 

 to the comparative age of the Newfoundland Banks. Lieut. 

 Payer ^ has observed respecting them : — " It is an established fact 

 that ice-bergs and ice-fields laden with the dibri^ and rubbish of 

 Arctic lands, deposit these burdens round the outer edge of the 

 Frozen Ocean, and to this process, partially at least, the origin of 

 the Newfoundland banks is to be ascribed." It would seem from 

 these observations that these banks have been formed since the 

 glacial period, hence that they are more recent than the Ber- 

 mudas. On the above grounds, therefore, it is but reasonable 

 to conclude that the Bermudas plant has superior claims to that 

 of the Newfoundland banks to be considered as the parent-stock 

 of the Atlantic plant. 



That the parent-stock originated in the Atlantic, and then 

 found its way into the Indian and Pacific Oceans is, at least, 

 doubtful, especially as a form of the plant called var. Capilli- 

 folium,' bearing fruit abundantly, has been found at Mauritius 

 by Col. Pike. Thus, then, in two oceans out of the three, S. 

 bacciferum has been obtained in fruit, but with sufficient differ- 

 ences in the forms to constitute varieties ; whether the Bermudas 

 plant differs from the others I have not been able to ascertain. 



Prof. Mertens (see his work on the algre collected by the 

 Prussian expedition to Eastern Asia) supposed that Sarg. denti- 

 folium, of the Red Sea, was the parent-stock of the floating 

 Sargassum, on the groimd that the same species of polyzoa were 

 found on both plants. Not a very strong argument, especially 

 as a remarkable difference exists in the structure of the 

 two plants. S. dentifoliutn has a serrated midrib, while that 

 of S. bacciferum is plain. This difference was observed by Prof. . 

 Agardh, who, in addition, expressed his belief * that ^. denti' 

 folium, an inhabitant of a tropical sea, could not make, or sur- 

 vive, the voyage round the Cape of Good Hope. It must then 

 have had other means of making the voyage, as the plant has 

 actually been found at Key West, Florida, by Dr. E. Palmer. 

 Dr. Farlow,^ who mentions this fact, observes: "It is not 

 stated whether it was floating or attached. Dr. Palmer's speci- 

 mens are more luxurious than those of the Red Sea, but the 

 serrated midrib seems sufficiently characteristic to warrant us in 

 supposing that the species is the same." Here then we have 

 another instance of a tropical plant being found in both hemi- 

 spheres. How did it get there ? 



According to the present conformation of the land in tropical 

 and sub-tropical seas, there is no water-pass^e open in those 

 latitudes between the Atlantic and Pacific, or between the 

 Atlantic and Indian Oceans. In the north and also in the 

 south, round " the Horn," the extreme cold would be fatal to 

 all the species of Sargassum ; and although certain species of this 

 genus grow at the Cape of Good Hope, S. bacciferum has 

 never yet been brought home from thence.' The presence of the 

 plant in the warmer parts of the three great oceans where means 

 of communication are now impossible, except between the Indian 

 and Pacific Oceans, owing to the conformation of the land and 

 climatal obstructions, remains still to be accounted for. This 

 can only be done by referring to a time when Mexico was sub- 

 merged, and the isthmus not yet in existence, and there was 

 thus communication between the tropical Atlantic and Pacific ; 

 when open passages also existed between the Indian Ocean and 

 the warmer parts of the Atlantic, and between the Indian and 

 Pacific Oceans. Tropical and sub-tropical algae would thus be free 

 to pass from sea to sea. That these plants did so is the opinion 

 of botanists and other scientific persons. In support of this 

 opinion may be mentioned the occurrence of a considerable 



^ Aikencettm for December i, 1877. Review of voyage of the Challenger. 

 ' " New Lands Within the Arctic Circle," vol. i. pp. 41, 42- 



3 I am indebted to Prof. Agardh for a fragment of a specimen of S. iac- 

 cifetum from the banks of Newfoundland, and to Dr. Oliver, of Kew, for 

 a fruitful specimen of Col. Pike's plant. 



4 Agardh, I.e. 



5 " List of Marine Alga: of the United States, with Notes of New and 

 imperfectly-known Species." By G. W. Farlow. From Proceedings of 

 the American Academy of Arts and Sciences, presented March 9, 1875. 



6 Agardh, /. c. 



