66 



NATURE 



[July 21, 1910 



Though retained in elementary expositions, serious 

 science has abandoned it for ever. 



The image B (1870 to i8go) left entirely on one 

 side the conception of a special electrical substance, 

 and sought to explain electrical phenomena by the 

 properties of the aether alone. But although this pic- 

 ture enabled one to form a representation of radiant 

 electrical energy, it, too, has been found insufficient 

 to explain a great number of phenomena. 



The image C is based on the notion of electrons, 

 and forms, to some extent, a combination of A and B. 

 It supposes the existence of a special substratum, and 

 preserves the idea of modifications produced in the body 

 of the aether; but the electrical substance is now con- 

 sidered as the origin of these modifications in the sether. 



We have summarised these distinctions because thev 

 characterise the entire fascicule. Prof. Chwolson 

 adheres to these distinctions throughout, and the re- 

 sult is that he is able to produce a final picture which 

 is more free from confusion than if he had attempted 

 to remove the dividing lines between them. Again, 

 the student will leave his perusal of these pages with 

 a far wider conception of the general lie of the land 

 than if one or other of these points of view had been 

 purposely blocked out. We do not wish to disparage 

 any recent books which emphasise one of these pic- 

 tures to the practical exclusion of others. They serve 

 their purpose. The pioneer is necessarily preoccupied 

 with his own line of march. But there is a danger 

 that, in the enthusiasm created by recent discoveries 

 and the success attending the contemplation of picture 

 C, the rest of the landscape will be forgotten. 

 We can wish for no better training for a student than 

 a perusal of Prof. Chwolson 's treatise. 



Of the general character of the book in its French 

 form we may say that we do not like it quite so well 

 as the German. The illustrations, which are taken 

 from the German translation, do not show up as satis- 

 factorily on the paper selected. But the production 

 of a French translation will be welcomed by many 

 to whom German is not intelligible; and it may be 

 said without any hesitation that, in the form in which 

 it now aooears, we have a text-book of physics which 

 is second to none in the French language.' It should 

 be in the library of every physical laboratory, and 

 students who are taking up the subject of physics 

 seriously will find it one of the best text-books of 

 which to obtain private possession. 



FLOWER POLLINATION. 

 Handbook of Flower Pollination. By Dr. P. Knuth. 

 Based upon Hermann Muller's work, "The Fer- 

 tilisation of Flowers by Insects." Translated by 

 Prof. J. R. Ainsworth Davis. Vol. iii. (Band ii.', 

 Teil ii., of the German edition). Observations ori 

 Flower Pollination made in Europe and the Arctic 

 Regions on Species belonging to the Natural 

 Orders. Goodenovieee to Cycadeje. Pp. iv + 644. 

 (Oxford : Clarendon Press, 1909.) Price 28^. net. 

 "W"OL. III. of the English translation, which has 

 V now appeared, concludes that portion of Knuth's 

 handbook for which that author was himself respon- 

 sible. The later volumes, issued afler Knuth's death 

 NO. 2125, VOL. 84] 



by Dr. E. Loew, deal with observations on flower 

 pollination made beyond the confines of Europe, while 

 the earlier volumes contain the observations made in 

 Europe and the Arctic regions, vol. iii. dealing with 

 species belonging to the orders Goodenovieae to 

 Cycadaceas. 



The English translation, appearing, as it does, ten 

 years after the publication of the original German 

 edition, has been brought up to date in many respects. 

 The arrangement of the Natural Orders has been 

 altered in consonance with more recent classification, 

 and some Orders have been merged as Sub-orders in 

 the larger Families. In many instances new observa- 

 tions have been added, and additional literature is 

 referred to, as, for instance, in the case of the prim- 

 rose, the pollination of which has been much disputed, 

 and also in the case of Pentstemon, of which genus 

 Loew has latterly made a very considerable study. 



This volume, like its predecessor, must be regarded 

 as a most valuable book of reference, yet here and 

 there are points of more general interest to 

 which, perhaps, reference should be made. On p. 434, 

 when dealing with the flower of the snowflake 

 (Leucojum), Knuth gives an interesting summary of 

 the method he has adopted to detect the presence of 

 a nectary, when the position of that organ is not 

 obvious at first sight. By suitable treatment of 

 flowers with Fehling's solution or Hoppe-Seyler's 

 sugar reagent he was able to detect the nectar- 

 secreting part of most flowers. Sometimes even fairly 

 conspicuous flowers, as, for instance, those of 

 Pyrola iiniflora, were found to be nectarless, and in 

 this case, though the flower is otherwise obviously 

 adapted to insect pollination, no insect visitors are 

 recorded in the handbook. Indeed, this volume, like 

 the preceding one, would yield much valuable infor- 

 mation to anyone in search of opportunities of enrich- 

 ing botanical science by accurate observations in the 

 field, for a number of plants, some of them quite 

 common, still require their insect visitors to be re- 

 corded. 



Some of the orders, like the Ericaceae, are of 

 interest, because in some genera, e.g. Calluna, Erica, 

 and Cyclamen, the flowers, though adapted to insect 

 pollination, and very eagerly visited by insects, are 

 during their later stages anemophilous, the pollen 

 becoming dry and powdery, and being readily carried 

 by wind. On the other hand, some flowers normally 

 adapted to wind pollination, like the sweet chestnut 

 (Castanea), also attract insects, and are no doubt 

 pollinated by them. 



The translator has omitted to note the observations 

 made recently on the dog's mercury (Mercurialis), 

 which indicate that this plant is provided both with 

 nectaries and sticky pollen, so that though apparently 

 anemophilous, and probably at times wind pollinated, 

 it is adapted to the visits of insects, and, as Knuth 

 records, is often visited by them. 



The anemophilous Graminese, too, ofl'er many 

 points of interest in connection willi the frequent 

 occurrence of cleistogamy and self-pollination of their 

 flowers. Insect visits are occasionally observed in 

 this group. Ludwig considered that the succulent 

 shining lodicules of many grasses sometimes 



