Oct. 2 2, 1874] 



NATURE 



503 



begins to move, not to move in the usual way (that which is auto- 

 matic during Ufe), but in an unusual manner, which must have 

 been very rarely, if at all, used during life, and when used must 

 have been purely conscious and voluntary ? I think I cannot 

 be mistaken in considering this to require some explanation. It 

 may be that the frog is constantly, during life, crossing one foot 

 over to rub the opposite side of the body ; but we cannot accept 

 this as an explanation unless it has been observed to be a fact. 

 What puzzles me is, that Prof. Huxley, Dr. Carpenter, and Mr. 

 Darwin, all refer to this case as an example of reflex action, and 

 none of them see any difficulty in it, or seem to think that it 

 requires any more explanation than the remaining quite intelli- 

 gible cases. As others may, like myself, feel the difficulty I 

 have endeavoured to point out, I hope some of your physio- 

 logical correspondents will enlighten us if they can. 



Alfred R. Wallace 



Supernumerary Rainbow 



In Mr. Backhouse's letter (N.\ture, vol. x. p. 437) he remarks 

 that the supernumerary rainbow is commonly seen only in the 

 upper part of the arch. Dr. Thomas Voung, in his I3akerian 

 Lecture ("Works," vol. i. p. 1S5, or Phil. Trans. 1S04), after 

 explaining the supernumerary bow by interferences, quotes a 

 paper in vol. xxxii. of the Phil. Trans., in which Dr. Langwith 

 describes his observation of a supernumerary bow on August 2 1, 

 1722 ; then remarks : " I have never observed these inner orders 

 of colours in the lower parts of the rainbow. I have taken notice 

 of this so often that I can hardly look upon it as accidental ; and 

 if it should prove true in general, it will bring the disquisition 

 into a narrow compass ; for it will show that this effect depends 

 upon some property which the drops retain whilst they are in the 

 upper part of the air, but lose as they come lower and are more 

 mixed with one another." But I am nut aware that anyone has 

 ever remarked an appearance which struck me on seeing a few 

 days ago a very complete primary and secondary bow with a 

 portion of two supernumerary bows within the primary and about 

 the highest part of the arch. To my eye the supernumerary bows 

 were not concmtric with the primary. My son agreed with me 

 as to this appearance when I pointed it out to him ; yet I thought 

 it was probably an illusion till the following explanation occurred 

 to me. 



The rain-drops may be presumed to be smaller high in the air, 

 and to increase as they descend. 



Now, the smaller drops produce wider interference fringes than 

 the larger drops do. Hence the supernumerary bow is widest 

 and therefore farthest from the primary at the top of the arch, and 

 gets narrower and nearer to the primary as it descends the arch 

 on each side, and " in the lower parts " ultimately fines away to 

 nothing. According to this theory the supernumerary bow is 

 not always concentric with the primary, nor indeed circular. 



It should be observed that another reason for the interference 

 bow being seen most frequently at the highest part of the bow is 

 that the small drops high in the air are probably more uniform 

 i in size than the larger drops lower down. 



Oct. 8 Joseph Blackburn 



Colour in Flowers not due to Insects 

 The doctrine that the conspicuous colours of flowers are 

 entirely due to the necessity for cross-fertilisation by the agency 

 of insects seems to be taking the world by storm. It is sup- 

 ported by Mr. Darwin and Sir John Lubbock. It could scarcely 

 be put forward on better authority. Yet there are several facts 

 with which it does not harmonise. For instance — 



1. Cultivation increases the size and colour of flowers quite 

 independently of the existence or non-existence of insects. 



2. Double Jlo^i'ers in which the doubling arises from metamor- 

 phosis of stamens or pistils are more showy than the single forms, 

 yet insects can be of little use to them, since they arc either 

 partially or entirely barren. The double-blossomed cherry is 

 brilliantly conspicuous, but it bears no fruit. 



3. Such abortive Jlo'^oers as the cultivated Guelder Rose and 

 Hydrangea depend for their beauty upon the destruction of the 

 reproductive organs. If their increased splendour is meant only 

 as a lure to insects, it is surely an absurd failure. 



4. The autumn colours of leaves and fruits can serve no such 

 purpose, yet these are often as bright and conspicuous as the 

 flowers of summer. 



5. Fungi and lichens exhibit brilliant colours, which can have 

 toothing to do with insect-fertilisation. 



Do not these facts indicate that though insects may be 

 attracted by conspicuous colours, and may have some influence 

 in the maintenance of coloured species, there is yet a deeper and 

 more permanent cause for the colour itself ? 



Leicester, Oct. 11. F. T. MoTT 



Habits of Squirrels 



Would you permit me to ask of your readers a question or 

 two upon the habits of squirrels ? I have had one in my posses- 

 sion, from the age of three weeks, for more than two years. I 

 have noticed that whenever it cleans itself, after licking, it sneezes 

 violently three or four times into its forepaws, then rubs them 

 thus damped over its fur. It seems to have the power of sneezing 

 at volition. 



Now, is this habit of sneezing, for the' purpose of cleaning 

 itself, a habit peculiar to squirrels ; or is it shared by other 

 animals ? 



I notice also that frequently when it is going thoroughly to 

 clean itself it jerks its forepaws over its ears, bringing them back 

 over its eyes, and always causing a milky liquid to suffuse the 

 eyes. This liquid swims over the eye, and then is absorbed. I 

 have thought that it may use this secretion also for the purpose of 

 moisture. The animal is in perfect health and splendid con- 

 dition. 



A squirrel I had three years ago also had this habit, though in 

 a slighter degree. D. T. 



THE NEW VINE-DISEASE IN THE SOUTH- 

 EAST OF FRANCE 

 I. 



WE have before us the Reports presented to the 

 French Academy of Sciences by the delegates of 

 the Cotiimission appointed by that body to investigate the 

 phenomena of the new and terrible disease of the vine in 

 the south-east of France — a disease which is fraught with 

 the most serious consequences to the material prosperity 

 of that country, which depends on its wine as a source of 

 national wealth not less important than are our coal and 

 iron to us. 



It was in the autumn of the year 1871 that the Academy 

 of Sciences directed special attention to the communica- 

 tions which poured in upon it from all quarters relative to 

 the ravages of the new parasite of the vine in the South of 

 France ; and at the sitting on the 25th September in that 

 year, it charged a Commission, consisting of M. Dumas 

 as president, MM. Milne-Edwards, Duchartre, and 

 Blanchard, to investigate the means of coping with the 

 disease. The Commission examined with the greatest 

 care all the manuscripts and printed monographs which 

 were brought under its notice, and paid particular atten- 

 tion to the scrutiny of the leaves and the roots attacked 

 by the Phylloxera vastatrix (for such is the name which 

 has been given to the new insect), which had been sent 

 to it from different places in France ; and, with the object 

 of giving to its labours the active direction necessary in 

 such circumstances, it decided to confide the execution of 

 them to three delegates, viz. MM. Balbiani, Max Cornu, 

 and Duclaux, whose learned researches in zoology, 

 botany, and chemistry, suggested recourse to them, and 

 they were accordingly charged with the pursuit of all the 

 observations which the subject would allow of, on the 

 actually affected territory. 



It is worth our while, at the outset, to observe the thorough 

 and methodical manner in which an attempt has been made 

 to wrestle with this new enemy of the material welfare of 

 France, and the application of the resources of science to 

 unravel as exhaustively as possible the causes and manner 

 of extension of the invasion of the parasite from its first 

 appearance till the present time. We in England are too 

 apt in similar crises to neglect the practical employment 

 of scientific means, to depend on private and mdividual 

 exertions for the investigation and treatment of the 

 different causes which threaten the national wealth or 



