BOOK REVIEWS. 



To a genus of tropical Rubiaceae, of which some forty species had been 

 described, he has added sixty-five. The whole 105 species are here 

 described in good technical Latin, according to the requirements of 

 our existing International rules, under a grouping in two subgenera, 

 the latter divided into three sections, devised by the author. This 

 occupies fifty pages of the slim volume ; but purely descriptive botany, 

 especially when it deals with an unknown genus of no ascertained 

 economic import, has as a rule absolutely no interest for the general 

 public, and even the botanist puts it aside among books of reference. 

 Dr. Wernham, however, in less than twenty pages of Introduction has 

 invested his subject with the most profound biological importance, so 

 as to arrest the attention of any thoughtful student of plant history 

 or geography. Not only has he given us a full history of our know- 

 ledge of the genus, an excellent clavis to the species, a list of the 

 collectors of the herbarium material, and an account of the distribution 

 and critical characters of the various types, but he has correlated 

 structure, habit, affinity, and distribution in a manner which should 

 serve as a model to other monographers. The Rubiaceae are a large, 

 mainly tropical, but widely-spread family, gamopetalous and mostly 

 insect-pollinated, and thus presumably of comparatively recent origin, 

 geologically speaking. Most of the species of Sabicea are. Dr. Wernham 

 tells us, cHmbers of a most primitive type, scrambhng, without hooks, 

 tendrils, or any special devices, over the river-banks or other scrub 

 of the tropical forest. A few of them have, however, migrated into 

 the open savannah and become erect bushes, and among these are 

 the whole five Madagascar species, four at least of which are closely 

 related offshoots from the near kin of the East African S. arhorea K. 

 Schum. The great majority of the species are West African ; but there 

 is what has been termed a secondary centre of dispersal in Western 

 Tropical South America. Dr. Wernham has drawn up a most sugges- 

 tive diagram, showing the early divergence of the African and American 

 stocks, his Section Capitatae being almost exclusively African and the 

 Sessiles almost exclusively American. The exceptions are apparently 

 interesting examples of what Hewett Watson described as Convergence. 

 The anomaly — and such anomahes are of the utmost importance to 

 the phytogeographer — is S. umbrosa Wernham, from Colombia, the 

 one representative in the New World of the East African subgenus 

 Stipulariopsis. 



" British Orchids : How to tell One from Another." By Colonel 

 J. S. E. Mackenzie. Illustrated by Miss C. E. Talbot Ponsonby. 4to. 

 40 pp., with 10 coloured plates. (Unwin Brothers, London, 1914.) 

 5s. net. 



A conservative estimate would reckon some forty-three species of 

 British orchids, though Colonel Mackenzie only speaks of thirty-six. 

 Of these, eleven are figured in Miss Ponsonby's mostly excellent 

 plates. These plates are mounted on tinted paper, and the book is 

 beautifully printed and tastefully bound in buckram, so that it is 



