Feb. 20, 1879] 



NATURE 



363 



LETTERS TO THE EDITOR 



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The Gulf- Weed {Sargassum bacciferum) a Means of Migra- 

 tion for Fishes and Marine Invertebrates 



Owing to the October number of Nature having been mis- 

 laid, I have not had an opportunity until lately of seeing Mrs. 

 Merrifield's remarks upon Gulf-weed which appear in vol. xviii. 

 p. 708, where the Bermudas are alluded to as a locality where this 

 species grows in situ. 



Having during my several visits to those islands of late years 

 paid some attention to the Sargassum and its inhabitants, per- 

 haps the few facts I am in possession of may prove interesting to 

 botanists, and those who study the geographical distribution of 

 marine animals. 



The Bermudas, being situate within that somewhat circular 

 area of the North Atlantic, formed by the currents of the Gulf 

 Stream, the North African, and equatorial currents, within which 

 exists that vast acctmiulation of weed known from the time of 

 Colmnbus to the present day as the " Sargasso Sea," afford excel- 

 lent opportunities for studying the plant in its floating condition, 

 and also adherent in its natural state to the reef. During the 

 winter months the prevailing gales, which are generally from 

 south-east to south-west, bring to the islands large fields, as well 

 as isolated patches, of the Gulf -weed, which prove a great boon 

 to Bermudan farmers, who, but for this ocean waif, would often 

 be minus manure sufficient to raise their root-crops with. To 

 an observer a field of weed coming in from sea presents a 

 somewhat variegated surface as regards colour, the major por- 

 tion of it being of a dark brown, interspersed with spots and 

 patches of light yellow. On closer inspection, these masses of 

 Boating weed are found to be inhabited by various species of 

 jjelagic and littoral crustaceans, particularly a small light brown 

 [crab, having a blotch of white on the carapace. Here and 

 ■there the eye rests on a little pearly-white object, the well- 

 Iknown shell of that almost unknown cephalopod, Spirula prO' 

 \totypus, of Peron. The pretty purple shell of lanthina cem- 

 Imunis is also to be seen, as are the singular forms of those truly 

 'oceanic acalephs, Valella communis and Physalia pelaqica, which 

 occasionally occur in large numbers, as they did dining a heavy 

 southerly gale on April 16, 186 1, when countless myriads were 

 literally wrecked upon the shores, together with the shells and 

 rafts of lanthinK. About the margins of these floating fields, 

 iwhich are of some depth, may be seen various species of fishes, 

 pnost of which have, no doubt, accompanied the fields, and lived 

 them, as game would do in a preserve where food and shelter 

 re found. There is one species of fish which, above aU others, 

 seems to belong to the Sargassum, viz., the Marbled Angler 

 \{Antannarius marmoratus), which, from its peculiar arm-like 

 Ectorals, is specially fitted to rest upon the weed. Here it 

 ikes its wonderful nest amidst the mass, suspended by means 

 Df those silk-like fibres, which prove amply strong enough to 

 iipport the large bunches of eggs, which hang like grape 

 Idusters within their orbicular case. These nests are occa- 

 sionally to be found, but cannot be considered common ; and 

 |only a few have been obtained from the weed on the Bermudan 

 lore. 

 There is hardly a doubt that it is from this fish-preserve in 

 Imid- Atlantic that those tropical and semi-tropical forms which 

 I occur incidentally at the Bermudas, Azores, Canaries, Madeira, 

 and also on the east coast of America, come, for I have fre- 

 iquently obtained from these masses of gulf -weed, species which 

 re not recognised as Bermudan, and would probably never have 

 "sited the island waters unless under the friendly shelter of the 

 Iweed. Moreover, I have observed even in heavy storms that the 

 never breaks throughout these floating fields, but although 

 leaving and swelling to the usual height, remains unruffled just as 

 lif oil floated on the surface. This absence of disturbance would 

 |of itself conmiend the field of weed to the fishes ; but when we 

 insider other suitable adjuncts, such as supply of food, and 

 shelter from enemies, we cannot fail to realise the excellent 

 leans of migration which this common possession affords, not 

 »nly to fishes, but to all kinds of those lower invertebrate forms. 



many of which have most certainly been brought to the shores of 

 the Bermudas by this means. The isolated patches of weed, 

 which follow the course of the Gulf Stream, and become broken 

 into lesser fragments, are also accompanied by those tropical and 

 semi-tropical fishes which are found almost every summer on the 

 coast of Nova Scotia, and even as far north as Newfoundland ; 

 and it is evident that without some such agency we could never 

 account for the abundance of certain southern pelagic fishes 

 which annually occur in our high latitude. 



In regard to the original habitat of S. btuciferum, as also the 

 origin of that vast mass of floating weed which exists in mid- 

 Atlantic, and is wholly composed ot this species, I fear we must 

 await further oceanic exploration. Although I am well aware 

 that it grows in certain places on the Bermuda shores, those 

 shores, even if they were wholly clothed with it, could not supply 

 a tithe of the material which forms the vast accumulation of the 

 weed existing in the Sargasso Sea. As to tke allusion in Mrs. 

 Merrifield's paper (quoting Agardh), made concerning the 

 S. bacciferum being an inhabitant of the banks of Newfound- 

 land, and other parts of the coast of north-cast America, I can 

 safely say that it is wholly unknown on this coast, save occa- 

 sional sprays, which are brought north by the Gulf Stream, as 

 are the fishes I have before alluded to. 

 ^ Halifax, Nova Scotia, January 25 J. Matthew Jones 



The Highest Tide on Record 



In Lyell's "Principles of Geology," tenth edition, 1867, 

 vol. i. p. 494, occurs a statement, given on the authority of 

 Admiral Sir F. Beaufort, to the eflfect that the tides at Chepstow 

 on the Wye sometimes rise to 69 and even to 72 feet. The 

 statement is familiar to all who have read Lyell's work. If it 

 be correct then this tide of 72 feet at Chepstow is apparently the 

 greatest in the world, that in the Bay of Fundy being given as 

 70 feet in the extreme. I can find no authority for a tide so 

 great as 72 feet at Chepstow other than that above cited. The 

 old "Bristol Channel Pilot" books of 1821 and 1839 say 

 nothing of the matter, as I am informed by Capt Tizard, R.N., 

 and the latest published " Pilot " gives 56 feet as the extreme 

 rise of tide at Chepstow. There is thus no official knowledge 

 of so high a tide as 72 feet, and I can find no published account 

 of Admiral Sir F. Beaufort's observations ; Sir C. Lyell refers 

 to none such. 



I should be extremely obliged to any reader of Nature who 

 can refer me to any certain record of exceptionally high tides at 

 Chepstow and confirmation of Sir C. Lyell's statement. There 

 seems to be some uncertainty as to whether the highest tides on 

 record occur in the British Islands or not. 



Exeter College, Oxford H. N. MoSELEY 



The Glacial Period and Geographical Distribution 



Prof. Asa Gray, in his very interesting lecture on the dis- 

 tribution of the forest trees of the northern temperate region 

 (Nature, vol. xix. p. 327), after pointiiig out the remarkable 

 differences that exist between the forests of the eastern and 

 western sides both of North America and the Old World, sug- 

 gests that the great poverty of the European as compared with 

 the Japan- Manchurian region in this respect was caused by the 

 Mediterranean cutting off the retreat of the flora which then 

 occupied Europe, as it retired, at the approach of the glacial 

 epoch, before the ice from the north. This explanation derives 

 considerable support from some other facts in geographical dis- 

 tribution. The most characteristic Alpine and Arctic butterflies 

 of the Palaearctic region belong to the three genera, Parnassius, 

 Chionobas, and Erebia. Of Parnassius, Dr. Staudinger, in his 

 latest catalogue (1871) enumerates [fourteen Palsearctic species, 

 of which three occur in North and Central Europe, ranging as 

 far south as the Balkans, but always in or near high lands, 

 about a dozen occur in temperate Asia, ranging as far east as 

 the Amur, and probably as many in North America, where they 

 also are truly Alpine butterflies. Of Chionobas one species {C. 

 aello, confined to the Alps) occurs in Central Europe, whilst six 

 or seven others range from Lapland over Russia and Siberia, 

 Mongolia, &c., to the Amur, and there are numerous species 

 in Arctic and Alpine North America. Of Erebia there are forty- 

 five Palsearctic species enumerated by Staudinger, and of these 

 no less than twenty-five occur in the central Alpine chains of 

 Europe. The genus likewise ranges all over temperate Asia, 

 going as far south as the Himalayas and Moupin, and in North 



