April 13, 1876] 



NATURE 



465 



smattering of the more recent development of the science. 

 Being thus completely furnished, he has entered the 

 arena. The result is altogether what might have been 

 expected. Inaccuracy of statement, meaningless defini- 

 tions, sins of omission and of commission, abound. If 

 anyone wishes to learn the rudiments of chemistry, let 

 him eschew this catechism as he would poison. 



M. M. P. M. 



Summer Holidays in Brittany. By Thomas J. Hutchin- 

 son. With Map and Illustrations. (London : 

 Sampson Low and Co., 1876.) 

 Mr. Hutchinson' is well known, among other things, 

 for his researches among Peruvian antiquities, and there- 

 fore, to his tour in Brittany he brought a trained obser- 

 vation. He has managed to write a very pleasant book 

 on rather a worn subject, a book which is likely to give 

 its readers a desire to follow the author's example. In- 

 deed it might form a verj' useful guide-book for the dis- 

 trict traversed by Mr. Hutchinson, and would have the 

 advantage of being much more pleasant reading than 

 guide-books generally are. Mr. Hutchinson evidently 

 made good use of his time when in Brittany, and to those 

 who have not read much on the subject the book wiU 

 furnish a great deal of information on the nature of the 

 country, the characteristics and manners and customs of 

 the people, the antiquities, historic and prehistoric, the 

 ecclesiastical and political histor\', and many other inte- 

 resting points. A very good map and some fair illus- 

 trations add to the value of the book. 



LETTERS TO THE EDITOR 



\Tlu Editor does not hold himself responsible for opiniotts expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. ^ 



Colour of Flowers Grown in the Dark 



In Nature, vol. xiii. p. 348, Mr. Thiselton Dyer gives an 

 extract from Sachs's "Text-book of Botany " to the effect that 

 no change is produced in the colour of flowers by growing ihem 

 ia the dark. This led to a letter from Mr. J. C. Costerus 

 (vol. xiii. p. 427), calling attention to the results obtained 

 Ijy Askenasy, published in 1876, wlio found that some kinds 

 were changed in colour, and some not changed. In the 

 autumn of 1873 I made a number of experiments on this subject, 

 and published a short accoimt of them in the same year in the 

 Quarterly Journal of Science, vol. iii. p. 474. I came to the 

 same conclusion as Askenasy has come to, and was also able to 

 establish some important generalisations. I will only mention a 

 few special instances, I was unable to cause any change in the 

 colour of the common Orange Lily {Lilium aurantiacum), 

 whereas I found that a very considerable change was produced 

 m the case of Erysimum Peroffikianum by only a moderate 

 degree of darkness. This may perhaps be owing to the fact 

 that the orange tint of these two kinds of flowers is due to entirely 

 different substances. That of the lily is due to what I have called 

 orange xanthophyll, whereas that of the other flower is due to 

 a much less stable compoimd, giving an entirely different spec- 

 trum, met with also in the orange marigold, and therefore 

 named by me Calendula xanthine. Comparing together the 

 mixed colouring matters found in an equal weight of die petals, 

 I found that the amoimt of the Caletuitda xanthine was only 

 half as great in the petals grown in the dark, whereas the more 

 yellow constituents were reduced only to three-quarters, so that 

 the general colour was more yellow. I found that a similar 

 change could be produced in the case of the marigold. If 

 shaded when the flowers are somewhat grown, the total colour 

 may be very considerably reduced without there being any 

 material change in the ratios of the different colouring matters, 

 whereas when grown in the dark from a very small bud, the 

 ratios are changed, as in the case of Erysimum. Growing 

 flowers in the dark seems to stop the normal development to a 

 greater or less extent according to the natiure of the colouring- 

 matters, the effect being the greatest in the case of those sub- 

 stances which are the most easily decomposed. We thus find 



what appears at first sight to be a very unlikely result, viz., that 

 those constituents which, when dissolved out from the petals, are 

 the most easily discolorised by exposure to light, are formed 

 in relatively greater amount when the flowers are grown in the 

 light, which is easily explained if we assume that a higher vital 

 power, depending on the presence of light, is necessary to over- 

 come the more powerful chemical affinities of the less stable 

 compounds. H. C Forev 



The Ash Seed Screw 



Mr. Stephen Wilson remarks, in his note on this subject 

 (Nature, vol. xiii., p. 428), '• Why the seed generally becomes 

 twisted as it dries is a very interesting question. But what 

 seems to me the most remarkable fact about this phenomon is, 

 that in every case, and in all trees alike, the thread of the screw 

 is in one direction." He also alludes to the uniformity in the 

 direction of torsion in the awns of two species of oat. Torsion 

 of all kinds occurring in plants is usually assumed to be due to 

 unequal longitudinal tension (see Sach's "Handbook," p. 770). 

 In a paper read before the Linnean Society, March 16, I pointed 

 out that the uniformity in the direction of the torsion cannot be 

 thus accounted for ; and a totally different explanation was 

 given of the twisting and imtwisting of the awns of certain 

 fruits (Avena elatior among the number) when they are dried 

 and moistened. It was shown that the power of torsion resides 

 in the individual cells of which the awn is constructed, and tha 

 it is by their combined action that the awn, as a whole, becomes 

 twisted in drying. It appeared to me extremely probable that 

 the same explanation woidd hold good for the twisted wing 

 of the ash fruit. I therefore boiled one in nitric acid and chlo- 

 rate of potassium, by which means the woody tissue is separated 

 into its constituent cells. These weie then teazed out on a slip 

 of glass and thoroughly dried over a lamp, and it was found that 

 many of them had become twisted on their axes ; and, which is 

 important, that they were all twisted in the same direction as 

 the fruit itself. This artificial drying represents the natural dry- 

 ing process which occurs during the ripening of the fruit. In 

 both cases contraction and consequent torsion result from 

 the loss of water, but in the natural process the cells not being 

 free to twist independently, are compelled to combine in pro- 

 ducing that torsion of the whole fruit which we are considering. 

 It is interesting to find the same principle holding good in the 

 case of the ash screw as in that of the awns of various Gramine^e 

 and Geraniaceas, and the twisted tails of the achenes in 

 Anenume montana. Moreover, I strongly suspect that the prin- 

 ciple of the torsion of an organ being dependent on the twisting 

 of its constituent cells is capable of wider extension, so as to 

 embrace the torsion of the stems of twining plants, &c. This 

 subject I hope immediately to investigate. 



Francis Darwin 



P.S. — The samara of the sycamore is a more efficient parachute 

 than that of the ash, but the wing has no appreciable twist, and 

 there is no uniformity in the direction of rotation assumed as the 

 fruits fall to the groimd. 



Down, Beckenham, April 4 



The Animal of Millepora 



It is a remarkable fact that during all the discussions on the 

 late L. Agassiz's statements regarding the animal of Millepora 

 some very careful drawings of it have been in the possession of 

 Major-Geiieral Nelson, R.E. They were done by himself 

 during his residence at Bermuda at the time when he was 

 writing that communication to the Geological Society on the 

 reefs and general structure of the islands which has made Lieut. 

 N'tlson, R.E., a name of mark. 



In common with most naturalists, I had expected that soon 

 after the Cliallenger reached Bermuda, we should have had a 

 satisfactory description of this very interesting polyp, so that the 

 truth, or the contrary, of Agassiz's description could be tested. 

 But it was not until July in last year that any commimication 

 relating to the subject was sent off firom the Cliallenger, the paper 

 being read on Nov. 25, 1875, at the Royal Society. Mr. 

 Moseley noticed therein that the examination of Millepora is 

 beset with serious difficulties, he, however, states that there are 

 large and small polyps, and that both kinds have tentacles, and 

 ' ' they appear to be four in number, and compound. " He 

 observes : " they are simply retracted by means of muscular fibres 

 which are arranged round the base of the cylindrical stomach 



