Augusi 23, 1877] 



NATURE 



339 



/ Across Central America. By J. W. Boddam Whetham. 

 (London : Hurst and Blackett, 1877.) 



[ This is a thoroughly readable and exceedingly instructive 

 narrative, by a capable observer, of a journey through a 

 country not often visited by travellers, and of which 

 English readers probably know little or nothing. Mr. 

 Whetham gives an interesting account of some of the 

 wonderful ruins which exist in Central Ameiica, and we 

 can commend his work to our readers as possessing both 

 novelty and interest. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correipond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts.l 



The Contractile Filaments of the Teasel 



The observations of my son Francis on the contractile fila- 

 ments protruded from the glands of Dipsacus,' offer so new and 

 remarkable a fact in the physiology of plants, that any confirma- 

 tion of them is valuable. I hope therefore that you will publish 

 the appended letter from Prof Cohn, of Breslau, whom every 

 one will allow to be one of the highest authorities in Europe on 

 such a subject. Prof Cohn's remarks were not intended for 

 publication, but he has kindly allowed me to lay them before 

 your readers. 



Extract from Prof. Cohn's Letter : — 



"Immediately after the receipt of your very kind letter of 

 July 26 I went to fetch Dipsacus, several species of which grow 

 in our Botanic Garden ; and proceeding after your recommenda- 

 tions, I put transverse sections of the cup-like bases of youni; 

 leaves, or the epidermis of these parts carefully removed from 

 the green parenchyma, into distilled water. I thus had the 

 pleasure of witnessing with my own eyes this most curious dis- 

 covery. First I ascertained the anatomical structure of the 

 pear-like glands which are rather elegant and remarkable. 

 From the basal cell rises the stalk-cell, in the second story 

 there are two cells, in the third four, and in the uppermost 

 series eight cuneiform cells converging to the centre, liut you 

 may conceive how much I was surprised by seeing the filiform 

 protuberances issuing from the apex of the glands ; it was quite 

 a perplexing spectacle. The filaments are, in their refrangibility, 

 very like the pseudopodia of some Rhizopods {e.g., Arcella or 

 Difilugia). I followed their changes for some time, and remarked 

 quite definitely, as I find described in the paper of Mr. Francis 

 Darwin how the protuberances slowly lengthen out, crook them- 

 selves hooklike or winding, and get knobbed either at the summit 

 or midway ; I saw the knubs or beads glide down the thread, and 

 at last be sucked into a globular mass adhering to the giand. 

 1 saw the protuberances always rise between the septa of two 

 or more adjoining cells, but nearly as frequently between the 

 lateral septa as on the apical centre. Generally there were many 

 protuberances on the same gland, pressed forvvard out ol dit- 

 ferent spots ; sometimes I saw two diverging branches proceed 

 from the same point like a pair of compasses, each behaving 

 independently in its changes. But the most curious appearance 

 in these protuberances was a constant waving undulation along 

 their extension, sometimes slower and perceptible with difficulty, 

 sometimes vigorous and quicker, but never ceasing ; more deli- 

 cate filaments appeared to me very like Vibrio, or the vibra- 

 tory flagella of some Infusoria. Not finding a special description 

 of the waving movements of the filaments m your son's paper, 

 I asked some of my pupils if they saw anything remarkable in 

 the filaments, without indicating what, but they all took the 

 same impression as myself. The only facts I have not yet been 

 able to witness of your son's discoveries are Figs. 6, 14, 15, and 

 tlie moniliform contraction ; nor have I yet found time to apply 

 chemical reagents, of which your son has made such good use. 



" Of course I am not able, after two days' inspection, to form 



* Abstr.-ict published in Proc. Roy. Soc, 1877, No. 179 ; published in full 

 in Quarterly Journal 0/ Microscopical Science. July, 1877. 



a definite judgment about the true nature of the fiUform protu- 

 berances. Putting aside the hypothesis of a parasitic Rhizopod, 

 there are two probabilities which still balance in my mind, 

 as clearly stated by your son. (i) The protuberances are secre- 

 tions of some colloidal matter, absorbing water, but insoluble 

 in it ; the movements are physical (not vital ones), the elonga- 

 tion of the filaments depending upon the imbibiiion, their con- 

 traction on the withdrawal of water by different reagents. There 

 are such substances, e.g., myeline, which shows rather similar 

 changes in water. Please also to repeU the experiments I 

 performed at the meeting of the British Association last year. 

 Into a cylindrical glass containing soluble silicate of alkali 

 (Waeserglas), diluted with half its amount of water, put a small 

 piece of crystallised chloride of iron ; from the fragment there 

 rises a hollow reddish tube growing upwards and moving very 

 quickly, like an Enteromorpha. But if you put into the diluted 

 silicate some protocliloride of iron (the latter is usually in the form 

 of a powder, but may easily be brought by gentle pressure 01 

 the fingers into crumb-like masses), then from the lumps there 

 arise innumerable filaments, very delicate and transparent, very 

 like the glass threads of Hyalonema, which rise in fascicules 

 vertically till they reach the surface of the lluid. 



" But I cannot deny that the general impression produced by 

 Dipsacus does not contradict the hypothesis that the changes of 

 the filaments are the vital phenomena of protoplasmic pseudo- 

 podia. 



" A French biologist (whose name I cannot just now 

 remember) has proved many years ago (I think in an early 

 number ol the Bull, de la Soc. Bot. de France) that the water in 

 the cups of Dipsacus is not a simple collection of rain in a 

 gutter, but a secretion of the leaf bases. If this be truly the 

 case, it is quite probable that the glands may have a special 

 adaptation for this purpose. Indeed, I should not hesitate to 

 agree with the vital theory, if there were any analogy known in 

 plauts. But further study of the phenomenon and the repeti- 

 tion of the chemical reactions which your son has already 

 indicated, will, I hope, in a short time enable me to form a more 

 decided judgment in this perplexing dilemma. 



" In the meantime I am happy to congratulate Mr. Francis 

 Darwin and yourself on account of the extraordinary discovery 

 he has made, and the truly scientific paper in which he has 

 elaborated it, and which has added a series of quite unexpected 

 facts to the physiology of plants." 



In a subsequent letter. Prof. Cohn describes what appear to 

 him as thinned points or pores in the cell wall of the glands from 

 which the filaments seem to be protruded. He also mentions 

 the very curious fact which he has discovered, that by adding 

 iodine to the detached epidermis of the leaf cups of Dipsacus 

 the whole fluid contents of the epidermis cells ttirn blue like 

 diluted starch paste, although no starch grains are met with in 

 any epidermis cell except in thestomata.' He adds that the 

 basal cell of the gland becomes blue, while the rest of it and the 

 excreted globules are stained yellow. 



I may add that I have heard from Prof Hoffmann, of Giessen, 

 that he formerly observed contractile filament of a somewhat 

 similar nature on the annulus of Agaricus muscarius. He has 

 described them in the Botanische Zeitung, 1S53, and figured them, 

 ibid., 1859, tab. xi. Fig, 17. CHARLES Darwin 



Down, Beckenham, August 15 



Relations between Sun and Earth 

 Prof. Balfour Stewart in the last of his exceedingly 

 interesting articles in N.^ture (vol. xvi. p. 45) on the suspected 

 relations between the sun and the earth, winds up with an appeal 

 (which I should like to see promptly responded to by the Govern- 

 ment here as well as at home) in favour of the establishment of 

 some institution to keep a daily watch upon the luminary that is 

 found to exercise such a marvellous control over terrestrial mag- 

 netism and meteorology. He also mentions incidentally the 

 discovery by Dr. Hunter that the famines in Southern India 

 have a period of recurrence which is nearly the same as that of 

 sun-spot frequency. This is no doubt an exceedingly plausible 

 hypothesis inasmuch as five out of the six years of drought 

 mentioned by Dr. Hunter as preceding the years of famine 

 ' Prof. Cohn adds that the blue coloration of the epidermis by iodine 

 occurs in the leaves of Omithogalum. 



