222 



NATURE 



[July 3, 1890 



Beyond the record of the appearance of these parts, 

 and the expression of our hope that the author will 

 speedily hasten the completion of his work, the useful- 

 ness of which will be greatly increased thereby, we have 

 nothing to add to our previous notice. 



LETTERS TO THE EDITOR. 



\The Editor does not hold hifnself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. 1 



Spiny Plants in New Zealand. 



In Mr. Wallace's recent work on "Darwinism," reference is 

 made to the absence of spiny and prickly plants in oceanic 

 islands in disproof of Prof. Geddes's theory that spines are an 

 indication of the ebbing vitality of a species. Mr. Hemsley's 

 remarks on the subject are quoted, and an explanation of the 

 occurrence of spines in our only species of Rubus and in 

 Aciphylla is given. In regard to the former it is stated (p. 433, 

 colonial edition) :— " In New Zealand the prickly Rtibus is a 

 leafless trailing plant, and its prickles are probably a protection 

 against the large snails of the country, several of which have 

 shells from two to three and a half inches long." The explana- 

 tion seems to me to be a very unsatisfactory one, and indeed to 

 be quite incorrect. The snails referred to (Placostylis bovinus, 

 Paryphanta Busbyi, and P. Hochstetteri) are very uncommon ; 

 I do not know that they occur at all in the South Island. The 

 Rubus, on the other hand, is everywhere a most abundant and 

 aggressive plant, springing up especially in bush clearings, whether 

 made by fire or by the axe alone. It is also incorrect to speak 

 of it as a leafless trailing plant. Sir Joseph Hooker, who is the 

 first authority on the New Zealand flora, has united all the forms 

 of Rubus found in these islands into one polymorphic species, 

 and even the most inveterate species-makers have never yet 

 successfully disputed his dictum. It must, however, be acknow- 

 ledged that four if not five very distinct varieties are included 

 under the common name of Rubus australis. Of these only the 

 variety cissoides of the " Flora Novse-Zealandiae " is leafless, its 

 leaves being reduced to prickly midribs. All the other forms are 

 leafy, some densely so, and these are by far the most abundant. 



The true explanation of the prickles is most probably that they 

 serve as climbing organs. No doubt all the developments of 

 the epidermis in the larger species of the genus Rubus served 

 primarily for protection against grazing animals. This is 

 evidently the case in the common raspberry. But even in the 

 various forms of the European blackberry or bramble, the 

 prickles seem to help the plants in their scrambling growth to 

 overtop those shrubs among which they grow. This is very 

 evidently the case with our New Zealand bramble, or "bush- 

 lawyer," as it is suggestively termed. It is a plant which grows 

 especially at the edges of the bush or in clearings, and it quickly 

 chmbs over the plants among which it lives. If we take hold of 

 a petiole (the stems have no prickles) we find it provided on the j 

 under side with a line of strong prickles, all curved downwards 

 so as to give them good holding power. Their catch is further 

 improved by the sharp bend in a direction opposite to their curva- 

 ture which the petiole and petiolules take. One has only to 

 attempt to pull a "lawyer " down from the plant on which it is 

 climbing to see that the snail-hypothesis is not the correct one. 



Any explanation of the formidably spinous leaves of Aciphylla 

 is at the best hypothetical. Perhaps the theory that they may 

 have gained their spines to prevent them from being trodden 

 down or eaten by the Moas, is as good as any other. In a paper 

 on the origin of the New Zealand flora, published in vol. xiv. 

 of the Transactions of the N. Z. Institute, I have made reference 

 (p. 496) to the scarcity of spiny and prickly plants. It is there 

 shown that in cases where such defensive modifications occur 

 the plants are either wide-spread in their distribution, having 

 probably, before spreading into these islands, acquired their 

 characters in other regions where they were of service ; or that 

 they belong to genera having extensive distribution. I have also 

 pointed out that in pungent-leaved plants, such as species of 

 Leucopogon, Archeria, &c., the strictly endemic species have lost 

 the pungent tips. The same remark holds as to the barbed 



NO. 1079, VOL. 42] 



spmes oiAca:na, which serve to distribute the seeds, probably by 

 mammalian agency. Of the seven described species two have a 

 wide distribution outside of these islands, and have strong barbs. 

 Iwo endemic species have the barbs not so well developed, 

 while in the other three species— also endemic— they are wanting 

 altogether. •' ** 



Can anyone offer any suggestion as to the formidable nature 

 of the stinging-hairs of our common ncWX^—Urtica ferox ? In 

 U.tnctsa&nd. U. australis the stinging-hairs are few in number 

 and feeble m their urticating properties. But U. ferox is a 

 species confined, as far as I know, to these islands, and it has 

 developed a formidable array of large and very poisonous hairs. 

 It IS worthy of remark that though so strongly protected in one 

 direction it is particularly liable to insect attacks, it being often 

 very difficult to find a perfect leaf. I cannot suggest any adequate 

 explanation. Geo. M. Thomson. 



Dunedin, N.Z., May 14. 



Drowned Atolls. 



As Captain Wharton speaks of the Macclesfield Bank as the 

 so-called "drowned atoll" of the China Seas, it may be in- 

 teresting to note that in the recent survey of it there were found 

 no less than 15 genera, including 27 species, of living corals 

 growing in depths from 21 to 44 fathoms, the dredge at each 

 haul always bringing up living specimens, and of these only four 

 were found growing on the more shallow rim of the Tizard 

 Bank. p. w. Bassett-Smith. 



As my opinion is that all the submerged atolls are in vigorous 

 growth, I concur, of course, in Mr. Bassett-Smith's view, in the 

 paragraph above, that the term "drowned," as indicating 

 " dead," is a misnomer ; and I inserted the words " so-called " 

 to express this. The examination of the Macclesfield and 

 Tizard Banks strongly supports this view. 



W. J. L, Wharton. 



The Essex Bagshots. 



Mr. H. W. Monckton has done good service in calling the 

 attention of geologists to the section through Brentwood Com- 

 mon (Nature, vol. xlii. p. 198) ; and I am glad to say that I 

 entirely agree with the interpretation of the section which b. has 

 suggested. The classification of all these beds as " Lower 

 Bagshot " is in fact but a repetition of the error committed in 

 former years in the Newbury country (see Q.J.G.S., vol. xliv. 

 pp. 178, 179). Lithological and palseontological evidence now 

 concur to prove what seemed to me in the highest degree 

 probable when the discovery of fossils in the Bagshot Beds at 

 Frierning was announced in the new edition of the " Geology 

 of London " last year, and what I suggested on general grounds 

 three years ago (see Geological Magazine, March 1887, p. 115) ; 

 namely, that iu the Essex area there is an attenuation of the 

 lower sands implying a transgressive relation of the " Bagshots " 

 to the London Clay, such as has been shown by me {Q.J.G.S., 

 vols, xliii, and xliv.) to occur along the northern margin of the 

 Bagshot area from Englefield Green to Farley Hill, south of 

 Reading. A Irving. 



Wellington College, Berks, June 30. 



A Remarkable Appearance in the Sky. 



The remarkable appearance in the sky noted by your 

 correspondent in Nature of June 26 (p. 198), as observed in 

 Sussex, on night of 17th inst., was also well seen here. I enclose 

 sketches which afford an approximate idea of the phenomenon 

 as observed on both the 17th and 25th inst. The former was 

 the first conspicuous occurrence here this season of those 

 "luminous boreal night-clouds," of which sketches have been 

 forwarded to Nature by the writer for some years past, but 

 from another locality of residence at a higher elevation. This 

 may account for failure of earlier observation during the present 

 year. The luminous forms have become less definite, the out- 

 lines being faint and nebulous, as contrasted with the bright 

 and definite cirro-form cloudlets seen when first noted, at con- 

 siderably higher altitudes above the northern horizon. 



Kensington, June 28. D. J. Rowan. 



