Nov. 29, 1888] 



NATURE 



I BOTANY OF SOCOTRA. 



iny of Socotra. By Isaac Bayley Balfour, IM.D., 

 .R.S., &c., assisted by other Botanists. Forming 

 oL XXXI. of the Transactions of the Royal Society 

 ■ Edinburgh. (Edinburgh : Grant and Son. London : 

 ''illiams and Norgate. j 888.) 

 NDER the auspices of the Royal Society of London 

 and the British Association for the Advancement 

 of Science, Dr. Bayley Balfour proceeded to Socotra 

 early in 1880, accompanied by Mr. A. Scott, a gardener, 

 and joined at Aden by Lieut. Cockburn, for the purpose 

 . of investigating the natural history of the island. Origin- 

 j ally it was intended that Colonel Godwin-Austen should 

 lead the Expedition, but circumstances prevented him ; 

 and the Committee, through Sir Joseph Hooker, thereupon 

 requested Dr. Balfour— who had recently completed an 

 account of the results of his botanical exploration of the 

 Island of Rodriguez-to undertake the task. He had just 

 been appointed to the Botanical Chair in the University 

 I ,of Glasgow, and the duties connected therewith demanded 

 iiis presence after the middle of April, therefore the 

 I .duration of the expedition was necessarily very limited, 

 I and the time actually spent on the island was little more 

 than six weeks, ending on March 30. Nevertheless, the 

 botanical collections included specimens of between five 

 and six hundred species of Phanerogams, besides Crypto- 

 gams ; though, as might be expected from the hasty 

 manner in which the work had to be performed, and the 

 short season during which the plants were collected, 

 many of the specimens were imperfect. The following 

 spring a party of German naturalists visited the island, 

 among them the distinguished African traveller and 

 botanist, Dr. Schweinfurth, to whom Dr. Balfour sent a 

 catalogue of the plants he himself collected, with the 

 gratifying result presently to be explained. 



Fortunately the German Expedition entered upon its 

 labours a fortnight later than the time when the British 

 Expedition finished its work. Vegetation was then at a 

 later stage of development ; and Dr. Schweinfurth was 

 able to supplement largely Dr. Balfour's botanical collec- 

 tions, especially in the direction of much more complete 

 material. The unselfish devotion to science displayed 

 by Dr. Schweinfurth is eulogized by Dr. Balfour in the 

 following words : — 



"With a generosity which is as pleasing as it is rare, 

 'lie subsequently sent his collections to me in England, in 

 order that the whole flora might be worked out in one. I 

 have already had opportunity to express publicly my 

 hvely appreciation of this act of friendship and self- 

 abnegation, and I wish here to put the fact again on 

 record, and to say how much Dr. Schweinfurth's specimens 

 have contributed to the satisfactory working out of the 

 details of the flora. The value of his collection must not 

 be measured either by the number of the species, or by 

 the species he found which we had not gathered. In the 

 excellence of his specimens and their completeness, and 

 the way in which they so frequently supplemented, in 

 flower and fruit characters, deficiencies in ours-therein 

 lay the value of Schweinfurth's plants, and I cannot 

 appraise it too highly." ' 



99 



Dr. Balfour elaborated the joint collections at Kew, 

 and it was announced in Nature five years ago that he 

 •had completed the descriptive part ; but delays in connec- 

 tion with the production of the plates, which need not be 



particularized, we are informed in the preface, prevented 

 the issue of the volume until this year. 



It is satisfactory, however, to be able to congratulate 

 Dr. Balfour and the Royal Society of Edinburgh on the 

 quality of the work now first presented to the public in a 

 complete form. Although it may fall considerably short 

 of being an account of all the plants that inhabit the 

 island, it is sufficiently full to be of the utmost value to 

 the student of systematical and geographical botany. 

 Dr. Balfour's 521 pages of letterpress are illustrated by 

 100 plates, drawn by W. H, and J. N. Fitch, Mrs. 

 Thiselton Dyer, and Miss M. Smith, though mainly by 

 the latter lady. Apart from the descriptive matter, the 

 geographical distribution of the individual species, and 

 the affinities of the flora as a whole, are given in ample 

 detail in the form of an introductory essay, which will 

 rank high among recent contributions to phytogeography. 

 There is also a map on a scale of about ] j inch to 5 

 miles, and a brief sketch of the position, physical features, 

 and geology of the island. 



Socotra is situated off the north-east corner of Africa, 

 about 500 miles from the entrance to the Red Sea, between 

 12° and 13° N. lat., and 53° and 54° E. long. Its extreme 

 length from east to west is about 72 miles, its breadth 20 ; 

 and it is about 140 miles from the nearest point of the 

 African coast, and a little more distant from the Arabian. 

 The surface is mountainous, the interior averaging 1000 

 feet in altitude, with granite peaks exceeding 4000 feet. 

 The main plateau is of limestone deeply cut into ravines 

 and valleys. In some places the hills rise abruptly from 

 the sea, in others there are intervening sand- plains several 

 miles in width. The climate is cooler and more humid 

 than in the adjacent parts of Africa and Arabia, and in 

 some parts there are perennial streams ; but the character 

 of the vegetation generally is that of a dry sterile country. 

 Out of 575 Phanerogams, or flowering plants, collected, 

 10, including the date and palmyra palms, orange, cotton, 

 tamarind, and castor-oil, were undoubtedly planted, and 

 many others weeds of wide dispersion ; whilst 206 are 

 apparently endemic ; and there are 20 endemic genera. 

 Unfortunately, as I think, Dr. Balfour has not deducted 

 the certainly and probably introduced species in his 

 analysis of the composition of the flora, hence his 

 figures representing the percentages of endemic genera 

 and species do not reveal the true facts. Thus he 

 calculates that 36-5 per cent, of the species, and 6-3 per 

 cent, of the genera, are endemic ; and these are high 

 percentages, considering the short distance the island is 

 separated from the mainland, and indicate a very ancient 

 flora ; but had he eliminated the species in question, these 

 percentages would have stood even higher. On the 

 other hand, it is a mistake to say (Introduction, p. xlix) 

 that the percentage of endemic species is about the same 

 as in Madagascar, where the proportion of endemic 

 genera is double that in the Socotra. The percentage 

 of endemic species in the Madagascar flora is probably 

 at least double that in the Socotran flora, and Mr. Barron, 

 in a paper he recently read before the Linnean Society, 

 estimated the endemic element at 80 per cent, of the 

 species. In British India it is as high as 68 per cent. ; 

 in Mexico and Central America combined it reaches 70, 

 and in the whole of Australia 80 per cent. 

 A comparison of the flora of Socotra with that of the 



