174 



NATURE 



[December 26, 1895 



apical glands, and the odour of the flower is rather weak, and 

 very disagreeable. In a cross of my own raising, the parentage 

 being P. Buonapartea x P. ccvrulea, the flower is delightfully 

 odoriferous, and the rays are tipped with glands, about half as 

 well developed as those of the former (the seed) parent. That 

 such is the case points to the possibility of the terminal cells of 

 the rays of such as P. utrulea being glandular in function in 

 some degree. The general structure of the ray is the same in 

 all, in respect of having conical epidermal cells, spiral vessels 

 running up to the apex, and bearing, besides numerous con- 

 glomerate crystals, so great a number of minute starch granules 

 as to render portions often almost black when treated with iodine. 



It was repeatedly proved that the perfume of my variety was 

 located in the rays — presumably the apices. It is singular that 

 certain hybrids studied, stated to be between P. alata and 

 P. cicriilea, e.g. Impiratrice Eugenic, do not bear any coronal 

 glands, for it seems likely from analogy (flowers not yet having 

 been observed) that P. alata should possess them ; one being 

 tempted to assume that species with long filaments at about right 

 angles to the corolla will be found to bear glands, while those 

 with shorter ones, lying at a small angle 

 with the corolla, will not. 



John H. Wilson. 



Yorkshire College, December 12. J'^' 



as mineralogists consider highly improbable. It is not proved 

 that the iridescence experimentally produced in the fossils is the 

 same as that occurring in a recent shell. As for Mr. Schwarz's 

 new objection, that the lamina; are not thin enough to produce 

 the phenomenon, this is certainly true for the calcite lamina;, 

 and is equally fatal to Mr. Schwarz's own explanation ; but some 

 of the conchiolin laminae are far thinner than the calcite, and 

 might well produce interference in the light reflected from their 

 upper and under surfaces. F A. Bather. 



December 12. 



Northerly Wind in Winter Seasons. 



The recent variations of northerly wind at Greenwich in a 

 series of the cold seasons October to March (the winds being re- 

 duced to the four cardinal points) present some interesting 

 features, to which I would invite attention. 



These variations, since 1841, are exhibited in the dotted curve 

 of the diagram (the ordinate figures expressing days) ; and a 

 smoothing process having been applied (averages of five), we 



Colours of Mother-o'-Pearl. 

 In your issue of October 24, Mr. C. E. 

 Benham calls attention to the fact that 

 the colours of mother-o'-pearl cannot be 

 due to the striations on the surface, as 

 originally explained by Brewster. I have 

 recently communicated a paper to the 

 Geological Magazine, June 1895, i" which 

 I came to the same conclusion, and also 

 found it impossible to accept the lamina 

 theory as stated by Mr. Benham, for the 

 following reasons. In certain fossilised 

 shells, notably those of the Ammonites, 

 the conchiolin of the shell has in course 

 of time disappeared, and there remains 

 not the lamina, but the prismatic struc- 

 ture ; hence I concluded that the latter 

 was the fundg.mental form in which the 

 calcite of the shell was deposited. In 

 Am. Ibex, Elisabetha:, &c. , the shell has 

 a chalky appearance, consisting of the 

 detached prisms which can easily be 

 separated by rubbing ; but when the 

 shell is carefully soaked in Canada 

 Balsam the interspaces become filled up 

 with the resin as they were in life, and 

 the play of colours is perfectly reproduced. 

 Where the original calcite has been 

 replaced by some other mineral, such as 

 silica or marcasite, as exemplified in the 

 Blackdown and Gault Ammonites, it is' 

 not the lamina, but the prismatic struc- 

 ture that is reproduced, and in both cases 

 the play of colours is similar to that of 



the original shell. In Meleagrina, whence the ordinary 

 mother-o'-pearl is derived, the prisms of the shell are not so 

 regular as those in the Ammonites, but the cause of the colour is 

 the same. The laminae of shell material, though very thin, are 

 hardly thin enough to produce the phenomenon as Mr. Benham 

 would have it. A full description of these prisms, and the way 

 they affect light, is given in the paper above referred to. 



Ernest H. L. Schwarz. 

 Cape Town, November 14. 



I AM indebted to you for giving me the opportunity of a 

 remark on Mr. Schwarz's letter. Interesting and valuable 

 though his researches were, the argument, as stated in the paper 

 to which he refers, did not carry conviction to me. To deduce 

 from fossils, in which secondary changes of mineralisation have 

 admittedly taken place, conclusions as to the minute histology 

 of recent shells, seems precarous. The connection between the 

 prisms and the experimentally produced iridescence is not clearly 

 proved J and the explanation of the supposed connection is based 

 on a purely hypothetical arrangement of calcite crystals, such 



NO. 1365. VOL. 53] 



(a) Dotted curve, variation in number of days of northerly wind, at Greenwich, in winter half (Oct., 

 March) ; continuous curve, smoothed with averages of five. (Here 1855, e.g., means Oct.-March 1845-5- 

 &c.) 



(1^) Sunspot curve (inverted). 



have the continuous curve (a). It will be observed that the 

 four long waves brought out more clearly by this smoothed 

 curve show a good deal of correspondence with those of the sun- 

 spot cycle, an inverted curve of which is given below {b). The 

 higher values of northerly wind seem to be more frequent, on 

 the whole, near sunspot minima, and the lower near maxima. 

 Does this point to a causal relation ? 



A few figures may be given. (For brevity we may designate 

 each cold season by the year in which it ends ; thus 1855 means 

 October-March 1854-55). 

 We find sunspot minima in 



1856 1867 1878 1889 



and maxima of the wind curves as follows ; — 

 Unsmoothed\ 1855 1870 



curve / (47) (45) 



Smoothed \ 1855 1869 



curve / (43'o) (37 '8) 



On the other hand we find sunspot maxima in 



1848 i860 870 1883 1893 



