27, i876] 



NATURE 



247 



nces, will be able to read infinitely grander legends 

 .. ild and mountainous scenery than he who looks upon 

 it alone through the glamour thrown over it by mythology 

 or genius. At all events, we welcome the spreading love 

 of travel as one of many signs of a great intellectual 

 awakening, although doubtless at present it has a good 

 deal about it which lays it open to the sneer of the cynic, 

 as have all new movements. There is a considerable, and 

 we think ill-natured outcry in certain quarters, that all 

 the accessible tourist grounds will become more and more 

 crowded by the followers of the beneficent Cook. But 

 there will always be some spot to which he who does not 

 wish to be counted one of the common herd of tourists 

 can retreat until he has gained vigour and nerA'e enough 

 to feel in a mood to mix again with " the kindly race of 

 men." Such a retreat is,, and wiU for long be afforded 

 by the "Abode of Snow" which Mr. Wilson and this 

 Lady Pioneer have so attractively described ; by and by, 

 no doubt, it will be made more accessible by roads either 

 from our own or from the other (is it premature to say 

 the Russian .'} side. 



LETTERS TO THE EDITOR 



\ Tki Editor does not kold kims^ responsible for opimons expressed 

 by his correspondents. Neitker can ke undertake to rdum^ 

 or to correspond tcntk tke writers of, refected manuscripts. 

 No notice is taken of anonymous communieaiions.] 



The Article " Birds "' in " Encyclopaedia Britannica " 



Mr. Garrod's article on the new edition of the " Encyclo- 

 psedia Britannica" in last week's NATUR.K contains the following 

 passage :— 



" As another example of the different teaching of the artificial 

 and the natural classifications, the Swifts {Cypsdida:) and the 

 Huaiming Birds ( Trochiiidu) maybe referred to. These twogroups, 

 I from the details of their internal structure when examined one 

 i by one, are most certainly related as intimately as are the Wood- 

 "" ^srs with the Toucans. There is, in fact, not a family 

 .ence between them, and yet, from their palates, Professors 

 ley and Parker place them in quite different dimions, be- 

 cause the vomer is truncated in the one and pointed in the 

 i other." 



j In a previous part of the article Mr. Garrod refers to my 



I paper on the Classification of Birds, published in the Pro- 



-"^^.ings of the Zool(^ical Society in 1867, which he criticises 



; he had studied it with a care proportioned to the labour it 



XcTcrtheless, I can but Xhvok. that his acquaintance with 



intents must be somewhat superficial, inasmuch as any care- 



eader will find at p. 459, the following passage under the 



head of Cypsdomorpha, or Swift- like birds : — 



i " This group contains three very distinct famihes — the Tro- 



.t- ; ■- tv^g Cypselid<z, and the Caprimnlgida. The first two 



. '-ve a length of the manus and a brevity of the humerus 



peculiar to themselves." 



Thus, so far from placing the Swifts and the Humming Birds 

 i IB " quite different divisions,'" I placed them in the same divi- 

 sion, and took pains to point out their close affinity ; and in 

 asserting the intimate relations of the Cypsdida and Trochilida, 

 Mr. Garrod is reiterating a view which, unless I mistake, 

 was first definitely pnt forward by myself, and not, as the 

 reaflers of his article woold be led to imagine, controverting my 

 -ions. 

 .'Ir. Garrod takes pains to show that " the structore of the 

 ikull does not alone suffice to determine the mutual affinides of 

 birds." The implication appears to be that Mr. Parker and I 

 assert t'ae contrary. I have no right to speak for Mr. Parker, 

 but 1 may remark that my knowledge of his works would not 

 have led me to Mr, Garrod's conclusion, while it would have 

 compelled me to treat any opinion of his, however much I 

 might be disposed to differ from it, in a manner different from 

 that adopted by Mr. Garrod. As to the facts, so far as I am 

 concerned, those who will take the trouble to read my paper on 

 ■""' ' ' ification of Birds, and an article by the editor of the 

 . a letter addressed to him by me, published in the 



1868, will see that the classification in question is not 



based upon cranial structure alone, and that, seven years ago, 

 we went a little deeper into the ques'ion of the principles to 



be followed in taxonomy than the point at present attained by 

 Mr. Garrod. 

 Jan. 23 T. H. Hcxley 



D-Line Spectra 



Is reply to a question propounded to you by a correspondent 

 (voL xiii. p. 224) as to my reasons for believing that sodium is 

 free in the dame of a spirit-lamp with salted wick, I have to 

 state as follows : — 



1. We now know that the flame exerdses a specific absorp- 

 tion, and is capable of producing dark D. If this were due to 

 vapour ot chloride of sodium, we should expect, in accordance 

 with what observation shows in other cases, Uiat solution of 

 chloride of sodium, or at least the solid chloride, would more or 

 less absorb the orange or yellow part of the spectrum, thongh 

 not in the same definite way, and we find it does not 



2. We know, by direct experiment, that vapour of solium 

 doss exert the very peculiar absorption indicated by dark D. 

 Different salts of the same metallic oxide agree in the mode in 

 which their solutions absorb Ught, or at least there is a strong 

 family likeness ; but when we pass from one oxide to another of 

 the same metal, there is a complete change. Much more 

 should we expect a complete change when there is such a pro- 

 found difference of chemical character as there is between sodium 

 itself and chloride of sodium. 



3. Lastly, Mr. A. Mitcherlich has proved, by direct expe- 

 riment, that vapour of chloride of sodium within a tube heated to 

 bright redness neither emits bright D nor produces dark D by 

 absorpti<m (/lgg?/nfor^'j AnnaIeH,Yol. Ii6, pp. 504, 505^. 



It need not surprise us that sodium should be temporarily free 

 in an ordinary dame, since the metal b prepared by heating car- 

 bonate of soda with charcoal, and in the flame we hare hydro- 

 carbons at a high temperature. Perhaps the heat alone woidd 

 suffice to set it free by dissociation. G. G. Storks 



Cambridge 



The True Nature of Lichens 



The editorial note on this subject in Nature, vol. xiii. p. 

 16S, was thoroughly disappointing to those who, like myself, 

 may have had hopes that the confident allusion by the reviewer 

 of Haeckel to the "clearing up"' of the "true nature of 

 Lichens" tuui reference to some demonstration — of which we 

 had not heard — of the part played by Spermogonia and Pycnidia 

 in Licken- Reproduction. Having long had in contemplation the 

 pubUcation of a volume of "Outlines of Lichenolt^'," it has 

 been my business for jrears to note carefully all publications of 

 any importance on the Natural History of Lichens, Those of 

 Prof. Schwendener of Bale and his disciples could scarcely have 

 escaped me ; so that I find the papers mentioned in the editoiial 

 note aforesaid, as well as others, duly recorded, with abstracts and 

 relative criddsms, in my Lichen ological memorandum book. 



My opinion of the speculations of Schwendener and his fol- 

 lowers has all along been, and still is, that so far from " clearing 

 up" the "true nature of Lichens," they introduce elements of 

 very decided confusion ; and that they are to be r^arded merely 

 as illostrations of German transcendentahsni, comparable to the 

 fanciful notions of his countryman Bayrhoffer, in 1S51, concern- 

 ing Lichen-Reproducuon. * The dermatic assertions of anonymous 

 critics concerning the "clearing up" of the "true nature of 

 Lichens/' by mere Speculations notwithstanding — I hold what I 

 have always held — that the Lichens as an O^er are quite as 

 natural, important, 'and distinct as any other Order of the Cryp- 

 tc^amia. And in so saying I do not foi^et the fact that they overlap 

 both the AlgaxaA the Fungi, On the contrary, I have over and 

 over again pointed out, in my own pubhcarions on the Natural 

 History of Lichens, the affinities, or points of affinity, between 

 Lichens, and Algje on the one hand. Fungi on the other. In order 

 that sight might not be lost of organisms of doubtfid character, 

 possessing elements of structure usually regarded as both algoid 

 and Uchenoid, or fungoid and hchenoid, or either the one or the 

 other, I long since proposed the establishment of intermediate 

 and provisional groups of Algo-lickenes atid Fungo-licketies. Such 

 groups would have the ad\'antage of attracting attention to those 

 passage-forms, which appew to me to be of 3ie highest interest 

 to the philosophical botanist. 



I have not myself had an oppertonlty of perusing Haeckel's 



* " Einiges uber lichenen und deicn Befruchtuag',' vob J. D. W. Bayr- 

 hoffer, Berr, 1851 ; aa fflnstnted 4tb. 



