258 



NATURE 



[July 13, 189: 



bad species, there still remains a large balance in its favour. It 

 has been better examined than any other part of the warm 

 Atlantic, but still we may attiibute this preponderance mostly 

 to the favourable natural conditions, principally the coral forma- 

 tion of large portions of its island shores. On the coast of 

 Africa there is not only no coral, but league after league of muddy 

 shore, making a marine desert so far as Algae are concerned. 

 The Indian Ocean comes next, with 514 species in 139 genera. 

 It possesses an enormous coast line, to a considerable extent 

 favourable to the growth of Ali^<'e (though including long desert 

 stretches) ; but the bulk of the records are from Ce)lon, 

 Mauritius, and ihe Red Sea, whileavery large proportion of ihe 

 region is unexati.ined. As in the West Indies, there is also 

 here a consideraLle proportion of bad species, principally 

 Sargassa, from ilie Red Sea. From the Cape we have 429 

 species in 141 genera. This rtmarka^^le total, fronr so short a 

 coast line, is obtained from Miss Barton's list in \he Journal of 

 Botany, 1893. The flora previously recorded in books amounted 

 only to 242 species in 99 genera, and ihii addition to its flora 

 has resulted from her examination of the British Museum 

 Herbarium, and her naming of the admirable collection made 

 by Mr. Boodle, at d al>o those made by Mr. .Scott Elliot and 

 Mr. Tyson. The most noteworthy ol servation on these aggre- 

 gates is the proportion of species to ger.eta. In the warm At- 

 lantic the genus averages well over 5 specie s ; in tl.e Indian 

 Ocean the proportion is nearer 4 ;han 3 sp'.cies to the genus; 

 while at the Cape it is almost exactly 3. This is instructive 

 when we remember, as I have elsewhere pointed out (Trans. 

 Biol. Soc. Liverpool, vol. v. p. 177), that whilethe Arctic Algie 

 average slightly more than 2 species only to the genus, the 

 West Indies and Australia average rather more than 5 and less 

 than 5 respectively. I estimate that the north temperate At- 

 lantic yields an aver.ige of about 4^ species to the genus, 

 and the difference between this and 3 species per genus found 

 at the Cape is to be attributed primarily to the short coast 

 line of the Cape, and in a less degree to its Algae being less 

 known. The calculation of such averages and proportions 

 appears to me to be jirstified only when applied to the whole 

 flora, and becomes more dangerous and apt to mislead when 

 applied to portions of it, since particular groups in all the (loias 

 have been subjected to unequal treatment by collectors and 

 describers, and we may perhaps trust to these personal errors 

 neutralising each other when the complete totals are compared. 

 The warm Atlantic and Cape have 85 genera and 114 species 

 in common, while he Indian Ocean and Cape have 86 genera 

 and 89 species in common. That the number of genera in 

 common should be so nearly exactly similar is interesting, and 

 to discover whether they are the same genera in many cases it 

 is only necessary to turn to the last table, where the hV^x com- 

 mon to all three regions are given to find that 72 genera are 

 common to all three. Some years ago I hazarded the speculation 

 that, while the genera of the ti opical Atlantic and those of the 

 Indian Ocean were largely the same, the species were, in a high 

 proportion, different ("Catalogue of Marine Al^x of the 

 West Indian Region"). We can now see that they have no less 

 than 103 genera in common out of a total of 139 occurring in 

 the Indian Ocean and 162 in the warm Atlantic. They have 

 certainly more species in common, viz. 173, but these must be 

 considered relatively to the two totals of 514 in the Indian 

 Ocean and 859 in the warm Atlantic, when nry expectation 

 will appear to be fairly borne out. Nevertheless, I 

 confess to having anticipated an even greater diversity of species. 

 That the absolute number of genera occurring at the Cape 

 should be by two greater than those of the Indian Ocean com- 

 pletely puzzles me. I cannot fully account for it on any theory. 

 While the number of species in common between any two of 

 the floras is greater than the number of genera (though in one 

 case only three more), the number of species, as might be 

 expected, in common to all three — viz. 59 — is less than the 

 genera — viz. 72. Again I should have expected to find rela- 

 tively fewer species in common. 



When one cjmes to analyse these totals, the process must be 

 carried on in a more guarried fashion. One expects, as shown 

 above, to find fewer species to the genus at the Cape than in the 

 tropical floras, but one hardly expects to find that the genera of 

 Floriiica at the Cape are by five more numerous than in the 

 warm Atlantic, and by 15 more than in the Indian Ojean. 

 There are no less than 95 genera of Floritk<v s.\. the Cape, with 

 29s species, while the goofthe warm Atlantic contain nearly 200 

 more species ! Matters are much the same in the case of the Phao- 



phytecc, and we have come to the Chlorophycea to redress the 

 balance in the case of the warm Atlantic. They just fail to 

 bring it level in the case of the Indian Ocean. It has teen re- 

 marked above that the genera which the two tropical floras have 

 in common with the Cape are almost identical in number. The 

 analysis shows that the figures are very steady, viz. 58 each of 

 Floridca, 14 and I'^oi rhctophyua, 11 each of Chlorophycea, 

 and two each of Frotophyc^a:, The table shows the tropical 

 character of such a group as the Siphonca very markedly. 1 hew 

 are 99 species in 23 genera in the warm Atlantic, 72 species ia • 

 16 genera in the Indian Ocean, and only 20 species in 7 geneia 

 :it the Cape. It is interesting to observe that the whole of the 

 16 genera of Siphoncir in the Indian Ocean are represented m 

 the warm Atlantic. It has no peculiar generic type of its owft 

 in this tropical group. While the genera of this tropical order 

 are thus practically identical, the species are in a very high pro- 

 portion diffijrent. Only 29 are possessed in common out of ite 

 two totals of 99 and 72. In the comparison of the tw o tropiciA 

 floras there is the coincidence that the genera and species rf 

 iiiphoneci s^ree exactly in numbers, viz. 16 and 29, with the tottd 

 of all the Phicofhycice — a thing without significance, however. 



The interest that is attached to the above comparison is mainly 

 this. We have here two tropical marine floras cut ofi' from each 

 o'her by a permanent continental area, and communica ing only 

 viA the Cape. That these floras have been periodically mingled 

 at the epochs of warmer climate at the Cape seems a reasonable 

 conclusion with regard to a group of such antiquity as thi; AlgX, 

 and the proportions of species in common and genera in cona- 

 mon between the different regions, and among all three m«T 

 have a significance in this respect to students of distribution [ff, 

 the totals <3\ Ziphonur, a peculiarly tropical order). I have el*e- 

 whrre (Trans. Biol. Soc. Liverpool, vol. v. p. 178) commented 

 on the fact that, " while in the Arctic and Australian regioBs 

 the PlurophycKT far outnumber the Chlorophycea, in the tropical 

 West Indian flora the proportion is very markedly reversed, and 

 the green t\\st outnumber the olive-brown. One is ten'pted 

 to put this down to the strottg illumination of the tropical sea, 

 but another reason is to be found in the fact that a number of the 

 Antilles richest as regards Alg.-r? are subject to irruptions ol fresh 

 and brackish water from the Orinoco floods — a condition that 

 would operate in the same direction." We can now check this 

 speculation by a comparison with the figures for the Indian 

 Ocean, mainly derived from such localities as the R:d Sea, 

 Ceylon, Mauritius, &c , in no case affected by the question rf 

 fresh-water floods. The figures for the Indian Ocean r.re ve»y 

 nearly the some for both groups — 24 genera and 117 species of 

 FlirrophycicT, and 26 genera ar.d 121 species of Chlorophyccce^ 

 thus showing indirectly that the irruptions of fresh water are, in 

 all probability, potent in the case of the West Indian Atg«. 

 One is much struck by the strength of illumination of the bottom 

 in a shallow coral sea, 1 ut the filtering action by sea walerof 

 the rays of light, and the interception first of those rays that are 

 most efficient in the work of assimilation — conditions modify^ 

 the pigments of Alga; — are the same in all seas.' The prarSt 

 cally tideless character of the Antilles would also make for a 

 preponderance of green over olive-brown forms. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 

 The Bristol Medical Sihool, which was established eatlyin 

 this century, has, since the establishment of University Colkgti 

 Bristol, about seventeen years ago, been aflfilialed to it, But 

 remained under the direction o,f a separate governing body. 

 Within the last few months the two institutions have been 

 amalgamated and placed under one Council, and the Medical 

 School now constitutes the faculty of nrtdicite in ibe 

 College. 



The Council of University College, Bristol, have raised to 

 the status of Professor, in the Faculty of Arts and Science, 

 Mr. F. R, Barrel!, Lecturer in Mathematics, and Mr. 

 A. P. Chattock, Lecturer in Physics, and have also appointed 

 Lr. Edward Fawcett, late Senior Demonstrator of Anatomy in 

 the Yorkshire College, Leeels, to the Professorship of Anatomy 

 in the Faculty of Medicine. 



1 Pccfnt research on orher pignrents by Prof. Marshall Ward inak«_ '^ 

 apf ear to me rr.ore probable that, ro rherase of the marirre Algie, th* pr8. 

 menls are ra;her shrelds against the excess of blue rays than acI.-iptatlorrs 10 

 hiighten rhe suscepllbilily of chlorophyll to the diminished surply of lire 

 others. 



NO. 1237, VOL. 48] 



