NATURE 



605 



IMURSDAY, OCTOBER iS, 1906. 



FLORAL BIOLOGY. 

 Iliindbook of Flower Pollination based upon Hermann 

 Mailer's work " The Fertilisation of Flowers by 

 Insects." By Dr. Paul Knuth. Translated by 

 J. R. Ainsworth Davis, M.A. Vol. i. Introduc- 

 tion and Literature. Pp. xix + 382; illustrated. 

 (O.xford : .'\l the Clarendon Press, 1906.) Price iSs. 

 net. 

 ^T^HE Clarendon Press is to be congratulated on the 

 i- appearance of the first volume of what is a 

 serious undertaking — the translation of a German 

 book in five volumes and nearly 3000 pages. 



Hermann Miiller's book " Die Befruchtung der 

 Blumen " appeared thirty-three years ago, and D'Arcy 

 Thompson's translation, published in 1883, has long 

 been out of print. English readers will therefore 

 welcome the present work, incorporating as it does 

 the great mass of research on floral biology which 

 has been carried out in recent years. 



The book appears under favourable conditions, 

 since the author— a recognised authority on the sub- 

 ject — has been able to come to an arrangement with 

 H. Miiller's representatives by which he is allowed 

 111 make use of all that naturalist's writings and 

 admirable illustrations. 



The chief feature in which it differs from Miiller's 

 books is the prominence given to the statistical 

 method of studying the visits of insects. This sub- 

 ject has received especial attention of late from 

 MacLeod, Verhoeff, Loew, Willis, Burkill, and others. 

 It was a department of study to which the author de- 

 voted much time, and in consequence his book con- 

 tains perhaps more on this subject than most readers 

 require. 



It is, as Prof. Balfour says in his preface, an 

 encvclopjedic work, and it has some of the defects of 

 its qualities. It is admirable as a book of reference, 

 and will be of great value to anyone desirous of 

 extending his knowledge of the subject ; but we con- 

 fess to missing what we expect in the introductory 

 volume of a handbook, namely, a broad treatment of 

 the subject such as is needed to introduce a student 

 to a detailed account of flower-pollination. There is 

 no effective discussion of what lies at the root of 

 the w'hole science of floral biology, namely, that 

 fertilisation at anv price is the primary necessity, 

 wliile cross-fertilisation is a secondary need. From 

 tliis standpoint the arrangements of the sexes in 

 plants become comprehensible as compromises between 

 the extreme cases of cleistogamy and diceciousness. 

 In one case fertilisation is assured, while cross- 

 fertilisation is im[)ossible; in the other fertilisation 

 is not a certainty, but if it occurs it implies of 

 necessity a cross between two individuals. Nor, 

 again, is the point of geitonogamy made clear, 

 namely, that if pollen is brought from a separate 

 flower there is at least a chance that it may come 

 from another plant. 



NO. 1929, VOL. 74] 



In referring to Darwin's "Cross- and Self- 

 Fertilisation," Knutli speaks of the paucity of the 

 experiments on crosses between flowers on the same 

 plant, but he neglects to mention what Darwin 

 thought the chief outcome of his work — the fact that 

 crosses between individuals grown under identical 

 conditions fail to give vigour to the offspring; and 

 this is a result that includes the effect of crosses 

 between flowers on the same plant. 



The need of a more generalised introduction to 

 floral biology was not so obvious to us in reading. 

 Knuth's book in German, but those who read it as 

 an English text-book, presumably intended for uni- 

 versity students, and who know the standard of 

 knowledge which such readers bring to the study, 

 will probably form a similar opinion. 



In the pages devoted to the history of the subject 

 a full account is given of the various ways of classify- 

 ing flowers from a biological point of view. Here we 

 find Hildebrand's and Axell's systems, of which the 

 second is not generally accessible to English readers, 

 being written in Swedish. Here, too, is Delpino's 

 interesting arrangement of typical floral mechanisms 

 into classes. Thus class iii., made up of flowers which 

 are visited by insects crawling into the tubular 

 corolla, contains the types named after the genera 

 Datura, Digitalis, Campanula, &c. In class vii. we 

 find one of the instances of the awkward translations 

 which occur here and there in the English edition. 

 The mechanism of Genista, Ulex, &c., is named by 

 Delpino "Forma a scatto," and this is rendered by 

 "tension form," which has none of the appropriate- 

 ness of the original and does not direct attention to 

 the explosion which is so characteristic of the type. 

 In other cases the translator is a little too literal. 

 What service is it to an English reader to find 

 Hymenoptera described as membrane-winged insects, 

 or Diptera as two-winged? 



Under the heading " Autogamy " a list is given of 

 all known instances of self-sterility; this, together 

 with the corresponding lists of heterostyled and 

 cleistogamic plants, forms a useful feature in the 

 book, .'^gain, in relation to cleistogamy, we are glad 

 to see a refutation of some of the supposed instances 

 of perpetual and unavoidable self-fertilisation, such 

 as the case of Junciis biifoniiis and of Salvia cleisto- 

 s;ama. 



.\ good deal of space is given to the various classifi- 

 cations of flowers according to their mode of fertil- 

 isation and the type of insect visitors. The best- 

 known system is that of H. Muller, who divided 

 them into flowers visited for pollen only, flowers with 

 exposed nectar, with concealed nectar, those adapted 

 to the visits of bees, Lepidoptera, &c. These classes 

 are known by the symbols Po, A, B, H, F, &c. 

 Knuth propounded a more elaborate classification for 

 which he had good reasons ; but why the translator 

 has altered the symbols so as to suggest the English 

 equivalents of the class-names we cannot understand. 

 Thus, instead of keeping Kl for " small-insect 

 flowers," he gives Sm as the symbol. This, except 

 on general principles, is no great matter; but when 



C C 



