Dec. 3r, 1874J 



NA TURE 



169 



successive layers of strata. That earthquakes are the 

 result of movement amongst these gases and liquids there 

 seems little reason to doubt. 



We gather, from the various accounts to hand, that 

 the characteristics of the recent typhoon were very 

 similar to those of the event of 1S71, viz., that it 

 came from an easterly quarter, and, after sweeping over 

 Hong Kong, reached Macao somewhat later, there culmi- 

 nating; and, describing a portion of a circle so as to pre- 

 sent all the appearances of a whirlwind, eventually dissi- 

 pafed itself along the coast upon contact with the high 

 land. This typhoon, as might have been expected, 

 crossed the estuary of the Pearl River from Hong Kong 

 to Macao in less than half the time occupied by the 

 typhoon of 1871. The distance is almost forty-five miles, 

 and the lowest readings of the barometer were as fol- 

 lows : — In Hong Kong at 2.15 A.M. and at Macao at 

 3.15 A.M. during 1874, against 11 P.M. and 1.30 A.M. 

 during 1S71. The rate of progression in the late instance 

 was moreover twice as great as that of the West Indian 

 hurricanes, which has been computed at twenty to twenty- 

 five miles per hour. 



Before we dismiss the subject it may not be out of 

 place to dwell for a few moments upon the probable 

 causes which give rise to these '" freaks of nature." At 

 Hong Kong the S.W. monsoon blows from April to 

 September, and the N.E. monsoon from September to 

 April. It is during the clian^c from S.W. to N.E. that 

 typhoons usually occur. The theory is this. When the 

 cold N.E. monsoon sets in suddenly it strikes upon a 

 vast tract of land in Southern China, and on a portion of 

 the China Sea warmed by the mild breezes of the oppo- 

 site monsoon, occasioning rapid precipitation or conden- 

 sation of vapours, and, as a necessary consequence, an 

 extensive vacuum where the rarefied air formerly was. 

 Other air then rushes violently in to fill the vacuum, and 

 strong breezes, sometimes developing into typhoons, are 

 the result. The mingling and collision of the various 

 currents at their point of contact also assists the dis- 

 turbance of the atmosphere. The reason of the gale as a 

 rule blowing from the east is apparent. Inland of the 

 coast line is a towering range of mountains, extending 

 down to Cochin China, and effectually arresting the rush 

 of air from that quarter. The open sea, therefore, is the 

 only free point of access. The prevailing direction of 

 typhoons at Hong Kong is, in point of fact, very nearly 

 that of the N.E. monsoon just commencing, but possibly 

 slightly diverted by the remaining influence of the oppo- 

 site monsoon. Hong Kong, Araoy, and Macao being 

 just opposite to the opening between Formosa and Luzon, 

 the full sweep of the wind rushes in unhindered towards 

 them from the Pacific Ocean. Macao, however, fares 

 worst, for it is situated precisely where the typhoon is 

 anested by the high land of the coast. The lowest read- 

 ings of the barometer are invariably therefore recorded 

 at Macao. 



ENCKE'S COMET 

 T HAVE received this morning, from the Observatory 

 ^ of Pulkowa, copies of Dr. von Asten's ephemeris of 

 this comet, in which the accurate effect of planetary per- 

 turbation to the approaching perihelion passage (about 

 April i3'o Greenwich time) is included. His positions 

 differ less than five minutes of arc from those I have 

 already communicated. The comet arrives at its least 

 distance from the earth on the night of i\Iay 3, about 

 which time it may be a bright object for the observatories 

 of the southern hemisphere. In these latitudes it will 

 probably be observed, as in 1842, to the end of the first 

 week in April. If not detected during the next period of 

 absence of moonlight, as I believe to be probable, there 

 can be no doubt of its visibility before the February moon 

 interferes. J. R. Hind 



Mr. Bishop's Observatory, Twickenham, Dec. 22 



FERTILISATION OF FLOWERS BY IXSECTS^ 

 IX. 



Alpine Ofchids adapted to Cross-fertilisation by 

 Butlerjlies 

 ■jVT O family of plants, as far as is known, offers more 

 ^^ various adaptations of flowers to insects of diiTerent 

 orders than the Orchids, which have called general atten- 

 tion to the relation between flowers and insects since the 

 admirable description by Mr. Darwin.^ Of thirty-four 

 species of Orchids found up to the present time in West- 

 phalia, five^ have been observed to be fertilised by 

 humble-bees, and partly also by other Apida; ; two ■* by 

 humble-bees and Diptera ; one" by species of Andrena'; 

 one "^by Vespa; one' by Apid.x>, Diptera, and Sphegido; ; 

 one* principally by Ichneumonida; ; one" exclusively l.y 

 Diptera; two^" by minute insects of different orders; 

 and four" by Lepidoptera. Although the fertilisers of 

 the sixteen remaining species '- have not yet been 

 observed, still it may fairly be deduced from the'structure 

 of their flowers that none of them, except, perhaps, 

 Habcnaria viridis, is fertilised by butterflies. Of thirty- 

 four species, then, growing in the plain and lower 

 mountain region, four, or at the most five, that is to say 

 12 to 15 per cent., are fertilised by Lepidoptera ; whereas of 

 five species of Orchids growing in the higher Alpine 

 region near the Ortler, three,'^ or perhaps fjur,'-* that 

 is to say 60 to 80 per cent., are adapted to cross-fertilisation 

 b\ butterflies, a proportion which strongly corroborates 

 my view that the predominant frequency of butterflies 

 in the Alpine region must have influenced the adaptations 

 of Alpine flowers. As two of these five species of Al- 

 pine Orchids are not mentioned in Mr. Darwin's classical 

 work, nor have yet been described with regard to their 

 contrivances for fertilisation, I will give here a brief 

 account of them. 



Gymnaaenia odoratissiina (Figs. 58, 59) produces its 

 honey in a nectary only 3.7 mm. in length, but the narrow- 

 ness of its entrance («' Fig. 59) proves it to be accessible 

 only to butterflies. These, when inserting their proboscis 

 into the nectary, cannot fail to attach to its upper side 

 the two viscid discs {d, d) which lie close together imme- 

 diately above the mouth of the nectary, and to which the 

 poUinia are fixed by their caudicles. Hence a butterfly, 

 when flying away from the flower first visited, bears a pair 

 of polHnia upright on the upper side of its proboscis. 

 When these are exposed to the air, the mem'oranous discs 

 to which their caudicles adhere contract (just as described 

 and drawn by Mr. Darwin at p. So of his work), which 

 causes the pollinia to move downwards and outwards in 

 such a degree as exactly to strike the stigmatic surface 

 when the butterfly inserts its proboscis into the nectary 

 of a second flower. 



Near the cataracts of Sie Adda, between the second 

 and third Cantoniera, 2,200 to 3,400 metres above the sea- 

 level, I found (July 14) plenty of these flowers, which, in 

 accordance with their name, struck me by their highly 

 .attractive sweet smell ; but although many butterflies 

 were visiting a large number of the surrounding flowers, 

 some of which were scentless, others but slightly scented, 



I Continued from p. 112. 



^ " On the various contrivances by which British and Foreign Orchids are 

 fertilised by insects." London, 1862. 



* Orchis Maria, O. mascnla, Epijiagum Gmdini, Caadycra re/'ois, S/i- 

 y. lathes autuinnaiis. 



■' Orchis jnacnltita,^ O. lati/alia. S Cvpripediuin calccatus. 



<^ Etipactis lati/alia. 7 Eptpactis palnstris. 



''Listera o-jaia. 9 Neattia nidus-avis. 



' ' Gymnadenia albida, Hcyminitim inanarchis. 



' ' Orchis pyrarnidalis, Gymnadenia canapsca, Platanthera hi/alia. r. 

 c'llorantha. 



" Orchis laxijiora, cariaphara, mililaris./iisca, and variegaia ; Hale- 

 Tiaria viridis, Ophrys muscifera and apt/era ; Cephalanthera pallens, 

 enst/olia, and rttbra ; Epipactis atroruhenSf viridijlara, and micraphylla ; 

 Ulalaxis patudasa, Liparis Laeselii. 



\\Migritella augustifalia, Gymnadenia. adoratissima,'c(:nopsea, and 

 all'ida ; Habenaria viridis. 



'^ Nigritella angtisti/alia, Gymnadenia odoratissima and canop:ea, and 

 perliaps Habenaria viridis. 



