54 



NATURE 



\May 15, 1879 



more highly specialised than in any existing flowers whatever ; 

 and if vre take into account the world-wide distribution of these 

 plants, their intense richness in genera and species, and their 

 wonderful complexity of structure, we must consider them as 

 among the most ancient instead of the most recent of flowers." 



Without venturing any opinion as to the geological age to 

 ■which the development of this wonderful order of plants must 

 be traced back, it seems to me that there are some classes of 

 facts concerning our naive European species which support the 

 conclusion that their existence in their present specific characters 

 must date from a very remote time. 



1. It is an important fact that out of fifty species of orchids 

 enumerated in Garcke's " Flora des deutschen Reiches " (exclu- 

 sive of the Bavarian Alps, which possess two or three more 

 species),'not less than forty-one occur in the British Isles (besides 

 Neotinea intacta and Spiranthes romanzoviana, not found in Ger- 

 many), a proportion considerably exceeding that of phanerogams 

 generally. Now, as it seems scarcely credible that orchids 

 should possess means of transportation across the sea in prefer- 

 ence to other plants, we must conclude that they inhabited the 

 British Isles before their separation from the Continent, which 

 involves that they occupied stations near the present coasts of 

 Germany or France previous to a great deal of plants that 

 reached these coasts only subsequently to the formation of the 

 Channel. These conclusions are rather strengthened by the fact 

 that several orchids are by no means frequent in Germany, and 

 very rare and local in Britain, which proves that their occurrence 

 is not to be accounted for by favourable present conditions, and 

 even renders it probable enough that some of the species found 

 in Germany, but not in Britain, may in the latter country have 

 become extinct in times not very long ago. 



2. Notwithstanding the light so plentifully thrown on the sig- 

 nificance of the floral peculiarities of our orchids by Mr. Dar- 

 win's admirable investigations, there remain some species whose 

 relations to insects, although evidently of a most specialised 

 nature, are yet very little understood. Such seems to be the 

 ca';e with Himantoglossum and with Ophrys. It is therefore to 

 be suspected that the adaptations of these species may point to 

 insects no longer existing in our countries. However, I should 

 not insist on this point were it not somewhat connected with the 

 following : — 



3. It has been observed by Mr. Darwin that "the frequency 

 with which throughout the world members of various orchidea- 

 ceous tribes fail to have theh flowers fertilised, though they are 

 excellently constructed for cross-fertilisation, is a remarkable 

 fact," And further on Mr. Darwin alludes to the unknown 

 causes which lead to the destruction of seeds or seedlings, form- 

 ing a check to the multiplication of orchids. Indeed, with many 

 of our native species, though abundantly fertilised, multiplica- 

 tion by seeds is evidently but a rare exception to the general 

 rule of propagation by side-bulbs, i.e., mere individual persist- 

 ence. Thus the wonderful contrivances for cross-fertilisation 

 point back to different conditions of life in the past, under 

 which their function must have been much more active and im- 

 portant than it is now. 



There may, I think, be found analogous cases in very differ- 

 ent quarters of the vegetable kingdom ; for instance, the frequent 

 reduction of the peristome of mosses to mere rudiments is pro- 

 bably connected with actual preponderance of vegetative propa- 

 gation over propagation by spores. In the orchids, too, there 

 are already perceptible some traces of a regressive change of 

 the apparatus for cross-fertilisation (for instance, in Ophrys 

 apt/era), as will be inevitable in the .course of ages, whenever 

 specialised structures are no longer sustained by active function, 

 leading to their reproduction under the agency of natural selec- 

 tion. Perhaps such regressive change goes on more slowly in 

 cases of merely vegetative propagation. 



Finally, I may allude to the fact of our native orchids 

 belonging to very different groups of the order, and this en- 

 hances the argument for antiquity, based on their geographical 

 distribution. D. Wetterhan 



Freiburg im Breisgau, May 10 



Barometric Pressure and Temperature in India 



In order to satisfy myself as to whether some of Mr. Broun's 

 conclusions (Nature, vol. xix. p. 6) held good when inland 

 stations were included in the comparison, I recently examined in 

 detail the pressure and temperature oscillations at fifty-one 

 stations in the Indian peninsula, computed from the means given 



in Mr. Blanford's "Indian Meteorologist's Vade Mecum." As 

 these stations represent every part of the country, the result* 

 afford a basis for deduction of sufficient extent to be reliable. 



An inspection of these shows (i) that the range of pressure- 

 oscillation corresponding to 1° F. varies very much at different 

 places, its extreme limits being 0*002 in. at Leh, and 0*032 at 

 Vizagapatam, and its mean value for all the stations o"oi7 in. 



2. That on arranging the stations in order of elevation, it is 

 plain that this variation is partly related to the height above sea- 

 level, being least at Leh (11 'SsS feet), the most elevated station, 

 and Increasing from thence downwards at the mean rate of about 

 o"oo2 in. for every thousand feet of descent. The numerous 

 deviations from this rule, however, especially at the lower eleva- 

 tions, make it evident that other factors operate besides height, 

 such as distance from the coast and latitude. Though no 

 rigorous comparison with these has as yet been made, a mere 

 insiiection of the results is enough to show that proximity to the 

 sea, and, therefore, ceteris paribus, greater humidity is associated 

 with a greater barometric oscillation corresponding to i* F." 



3. That when the element of horizontal space alone is con- 

 sidered, the pressure oscillatio;\ increases with the temperature 

 oscillation, but not very regularly, and that while this relation 

 holds pretty generally in the plains, it disappears altogether at 

 the more elevated stations, or, when the element of vertical space 

 is introduced. 



Now while the pressure ranges generally decrease pretty 

 regularly as we ascend, the temperature-range remains about the 

 same at different heights. The decrease, therefore, in the 

 pressure-oscillation for 1" F., noticed in the case of elevated 

 stations, must plainly be solely due to the contraction which 

 takes place in the pressure-range. 



The diminished mass of atmosphere above the more lofty 

 stations, doubtless in a great measure accounts for this diminished 

 amplitude of the oscillation. Another important factor, how- 

 ever, in this result, must not be overlooked, viz., the double 

 annual oscillation of monthly mean pressure which takes place at 

 stations of 6, 000 feet and upwards in height, apparently through- 

 out India, the effect of which is sensibly to diminish the absolute 

 annual range of pressure-oscillation at these heights. 



In fact, the curves representing the mean monthly barometric 

 pressure in the winter at the hills, and on the plains respectively, 

 may be taken to approximate more or lesi in character to those 

 in the adjoining figure. 



Nov. Dec. Jan. Feb. March April 



On the 1 

 plains, i 



Pressure Curve (the critical points are marked with asterisks). 



Now as the pressure on the plains is made up of the pressure 

 at a height of 6,000 feet -t- the weight of the stratum of air 

 between, it is evident that the latter must reach its maximum 

 somewhat later than December. Moreover, as the winter de- 

 pression at the highest stations is considered to be caused by the , 

 inrush at their level of the saturated anti-monsoon at this season,' 

 the direct effect of the cold of this season in increasing the den- 

 sity, and hence the pressure of the atmosphere, will only be felt 

 in the stratum of air between them and the plains. It is im- 



^ This relation appears to be independent of that due to elevation, with 

 which it might be thought identical, owing to the general decrease in the 

 heights as we travel seawards. The foilowine stations which have nearly the 

 same elevation, but are at widely different distances from the sea, will show 

 this very clearly : — 



Height above sea Bar oscillation 

 in feet. for i° F. 



Lucknow 369 o'oij 



Sibsagar 332 



0"028 



Difference 



37 



Now if the approximate rule for difference of elevation already mentioned, 

 viz., a decrease of o 002 inch in tie bar-oscillation for i* F. for every 1,000 

 feet of ascent be applied in this case, the decrease at Lucknow_ should 

 evidently be inappreciable. As it is, however, it is of very considerable 

 magnitude. 



" Vide "Indian Meteorologist's Vade Mecttm," by H. F. Blanfoni, 

 P-75- 



