NATURE 



zn 



THURSDAY, FEBRUARY lo, 1881 



ALPINE FLOWERS 

 Alpenblumen Hire Befruchtiiug dunk Insckh'it U)id ihrc 

 Anpassiingen au diisclhen. Von Dr. Herman Miiller, 

 Oberlehrer an der Realschule I. Cirdnung zu Lippitadt. 

 Svo, 611 pp. (Leipzig: W. Engelmann, 1S81.) 



THE naturalist who studies animals or plants in a 

 state of nature must often wish that he could test 

 his conclusions experimentally by varying the conditions 

 under which a given set of facts are observed. He 

 wishes that he could change the food of a grojp of 

 organisms, or the climate to which they were exposed, or 

 that he could diminish the numbers of one sub-group 

 while those of another were increased. As he cannot do 

 tliis he is obliged to be content with treating the facts 

 within his grasp in the spirit of an experimentalist, by 

 comparing large classes of facts as they occur under 

 different conditions. 



The present volume of Dr. Muller's is something more 

 than a descriptive study of the means of fertilisation found 

 among alpine plants, for it is an admirable example of 

 the kind of comparative investigation to which we have 

 alluded, and as such is an extremely valuable contribution 

 to the general science of plant-fertilisation. 



It is a difficulty inherent in such inquiries that the 

 observer, not having had a hand in varying the conditions, 

 has to discover exactly in what way the environments 

 differ in his two stations of observation. The most im- 

 portant feature in the environment of a plant considered 

 in relation to fertilisation is the manner in which it is 

 visited by insects. Thus an extensive knowledge of the 

 alpine and lowland insect fauna is a necessary part of Dr. 

 Hermann Miiller's inquiry. Nor is it eno.:gh to study as 

 an entomologist the relative frequency of bees, flies, 

 butterflies, &c., in the mountains and in the plains ; but 

 the observer must discover by long and patient observa- 

 tion the diflfeient manner in which these insects visit the 

 flowers in the two regions. The amount of this kind of 

 labour condensed into the volume may be guessed at by 

 looking at the long lists of insect-visits appended to each 

 plant described, or arranged in the statistical tables in the 

 latter part of the book. 



The collection of this mass of detail must have tried 

 Dr. Miiller's almost unbounded energy and patience to the 

 utmost. Several weeks in each of the last six summers 

 have been devoted to the research ; and the record of a 

 single day's work (which we are glad to find was a somewhat 

 exceptional one) will show how well the time at his com- 

 mand has been utilised. On this day, which was spent in 

 the Heuthal on the Bernina, he was surrounded by flowers 

 and insects from 8 a.m. to 4 p.m., during which interval 

 he made notes on the visits of 237 insects, 225 of which 

 were numbered and brought home. Dr. Miiller adds that 

 he was continuously spurred to the utmost of his powers 

 by the consciousness that numbers of insects were making 

 unobserved visits behind his back. 



Nor has his energy and ingenuity in classifying and 

 tabulating his results been less remarkable, as will be seen 

 by an examination of the twelve tables which are inter- 

 spersed in the latter part of the book ; in these tables 

 Vol. XXIII. — No. 589 



the visits of the various orders of insects to various kinds 

 of flowers in different localities are numerically compared. 

 It is not a little remarkable that the visits of insects, 

 which to the ordinary observer appear so casual and 

 lawless, should be capable of such strict and statistical treat- 

 ment. But it should be remembered that treatment of 

 this kind is only possible with the large mass of facts 

 which Dr. MiiUer has collected. 



The most striking facts in the book are those connected 

 with the predominance of butterflies in the alpine regions. 

 The changes which occur in the insect fauna as we ascend 

 are briefly that the relative number of Lepidoptera and 

 Diptera (especially the short-trunked flies) increase, while 

 the Hymenoptera and Coleoptera, as well as the other 

 unimportant kinds, diminish in relative number. Thus if 

 we compare the number of different visits made to flowers 

 in the lowlands and the alps,' we find the following pro- 

 portions : — 



LowL-inds Alps. 



Lepidoptera 100 614 



Diptera 100 109 



Hymenoptera loo 35'5 



the number of visits made by each order of insects in the 

 lowlands being taken as 100. 



One marked result is that classes of flowers chiefly 

 visited by bees in the lower regions are in the alps much 

 frequented by Lepidoptera. Thus, of a hundred different 

 visits made to Papilionacefe in the lowlands "j'i, per cent, 

 are those of Apidae, 17 per cent, are made by Lepidoptera, 

 so that in the plains they are markedly " bee-flowers." 

 But in the alps only 40 per cent, of the visits made to 

 Papilionacese are those of bees, and 56 per cent, are those 

 of Lepidoptera. The same fact was observed in the 

 Labiates and in a number of Composite flowers. The 

 adaptations which alpine flowers exhibit in relation to 

 this preponderance of Lepidoptera form some of the most 

 interesting parts of the book ; with some of the facts the 

 readers of Nature are already familiar, through Dr. Muller's 

 admirable articles on the subject which have appeared 

 in these pages. The principle which underlies these alpine 

 modifications may be illustrated by two sections of the 

 genus Gentian. In the first of these (Coelanthe) fertilisa- 

 tion is cft'tJCicd by humble-bees creeping inside the corolla. 

 This necessitates so wide a tube that Lepidoptera can 

 steal the nectar without effecting fertilisation. The 

 second section, Cyclostigma, is characteristic of the alpine 

 regions, and the flower has been adapted for fertilisation 

 by Lepidoptera. The passage by which the nectar is 

 reached is so narrow that the proboscis of the butterfly is 

 obliged to touch the anthers, and to effect cross-fertilisa- 

 tion. At the same time the tube in many of the Cyclo- 

 stigmata is so much lengthened that only such a long pro- 

 boscis as that of Macroglossus or of Deilephila can reach 

 the nectar. It is probable that the first steps towards the 

 development of closed nectaries were originally serviceable 

 to the plant in protecting the nectar from rain ; the flowers 

 being thus rendered more attractive, because the visiting 

 insects had a chance of finding undiluted nectar even after 

 a shower. The lengthening of the corolla tube in the above- 

 mentioned section of Gentians which protects the nectar 

 from all but a few long-trunked insects, confers the same 

 kind of advantage on the flower, for it is thus rendered 

 highly attractive to those insects which can alone obtain 



' x'lipine as used by Dr. Miiller means above the tree-limits. 



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