May 20, 1909] 



NATURE 



zi: 



THE FLOWERING PLANTS OF AFRICA. 

 Die BUiteupflanzen Afrikas. Eine Anleitung ziim 

 Bestimmen der Gattungen der Afrikanischen 

 Siphoiiogamen. By Franz Thonner. Pp. xvi+672 ; 

 with 150 plates and i map. (Berlin : R. Fried- 

 liinder und Sohn, 1908.) Price 10 marks. 



THIS is not the first attempt by the author of 

 making- keys on a large scale. In 1895 we 

 had from him an " Analytical Key to the Natural 

 Orders of Flowering- Plants," in 190 1 an " Excur- 

 sionsflora von Europa," essentially a key to the 

 genera of the flora of Europe, and now we find him 

 directing his energy in the same way to the whole 

 of the phanerogamic flora of Africa and the African 

 islands. If we consider that this flora includes 262 

 families and 3648 genera, the formidable character 

 of the task becomes at once apparent. No one can 

 possibly claim an intimate knowledge of so vast a 

 number of genera, and if some one came near to 

 it he would probably be the last to care for the 

 work. In fact, if the thing is to be done it is just 

 as well that the author should not know too much 

 of the details and of the real complexity of the 

 problem. General and rather extensive than inten- 

 sive familiarity with the families, sound judgment 

 in the selection of the authorities which supply the 

 material for the key, method, good memory, and 

 infinite patience will further the work more than 

 anything else. 



The book is distinctly one of those which must be 

 tried, and frequently tried, before it is possible to 

 judge whether they serve their purpose or not. In 

 this instance the object aimed at is to provide the 

 traveller or colonial in Africa, as well as the student 

 outside .\frica, with a key for the easy and correct 

 determination of the generic names of the African 

 plants. A general inspection of the book and occa- 

 sional checking on some of the more puzzling genera 

 have certainly created the impression that the author, 

 to a considerable degree, possesses the qualities 

 necessary for the task he has set himself. There 

 are, of course, blemishes and weak points; but they 

 are practically unavoidable, and it would be un- 

 gracious to insist upon them. On the whole, the 

 key — or, rather, the system of keys — works well 

 enough. Nobody expects more than a certain amount 

 of guidance from a key of such dimensions, particu- 

 larly when applied to a flora so rich and in many 

 aspects still imperfectly known. The difficulties with 

 which the key-maker has to contend arise mainly from 

 the overlapping and the varied combinations of char- 

 acters, the sexual heteromorphism and the dicecism of 

 flowers, and the so-called anomalous forms; they 

 are smaller towards both ends of the taxonomic 

 ladder, but really formidable where the families are 

 concerned. This accounts, no doubt, for the fact that 

 dichotomous keys to families on a large scale have 

 so seldom been attempted. To devise such a key 

 |)urely on- the basis of affinities, and so that the 

 units follow the same sequence as in the system, 

 is impracticable, and the author has very wisely not 

 hesitated to break up the families whenever neces- 

 sary, and to let them or their components come 

 NO. 2064, VOL. 80] 



in where the characters which were found most 

 workable bring them in. But if twenty-seven 

 families of Choripetalae are cut up, each into from six 

 to fourteen parts, and therefore appear in as many 

 different places in the key, one cannot help thinking 

 that the author has gone too far. The same applies 

 to a still higher degree when we find relatively so 

 homogeneous families as the Ericaceae, Apocynaceas, 

 and Convolvulaceae each in eight to ten places, and 

 the small families of the Pedaliacese and Plantagin- 

 aceae in six and seven places respectively. It ought to 

 be possible to focus, if I may say so, those families 

 far better. The author has freely used combinations 

 of characters, and, although much more rarely, con- 

 ditional alternatives. The key-links are in this way 

 apt to run into several lines, and we may occasionally 

 get impatient over having to read through them ; 

 but it pays in the end, whilst those terse and trim 

 apodictic keys which play with pairs of contrasting 

 characters, and allow barely one line to each link, 

 generally break down in practice. 



In establishments with large herbaria, where the 

 naming of African plants is part of the regular 

 routine, there will probably be little demand for the 

 book. On the other hand, it ought to prove very 

 useful vi^here the workers, without being especially 

 familiar with the African floras, have occasionally to 

 " run down " members of those floras, and particu- 

 larly so when the plants belong to families which have 

 been dealt with in the early volumes of the " Flora of 

 Tropical Africa " and the " Flora Capensis," volumes 

 which for completeness have long been out of date. 

 It is, however, a very different question whether the 

 ordinary botanically inclined traveller or colonial will 

 benefit very much by the book. As it covers Africa 

 from Algiers to Cape Town, and from the Canaries to 

 Madagascar, a very great portion of the work must 

 for either of them necessarily remain ballast, and the 

 traveller especially will feel little disposed to burden 

 himself with an extra 45 lb. on the chance of worry- 

 ing out a few generic names which he can, after all, 

 not verify on the spot. There remains of field-workers 

 only the professional collector, and he will probably 

 find it quite worth his while to take the volume with 

 him, provided he grasps the purely German ter- 

 minology, which, with the Latin equivalents, is ex- 

 plained in a glossary at the end of the book. 



The conception of the families and genera is, as 

 might be expected, that of Engler's " Natiirliche 

 Pflanzenfamilien," and in so far quite up to date, 

 whilst the recent English literature has perhaps been 

 considered less fully, witness, for instance, the reten- 

 tion of the West Indian genus Biovularia. A peculiar 

 feature of the work is the addition of not fewer than 

 150 plates representing types of as many distinct 

 families. They are throughout originals, and many, 

 if not most of them, portray species which had not 

 been figured previously. The habit figures which 

 we owe to the skilled and artistic draftsmanship of 

 Herr J. Fleischmann are as charming as they are 

 exact. They alone are worth buying the book for. 

 Analyses are added in all cases. They are, on the 

 whole, satisfactory ; but the absence of all lettering 



