July 28, 1887] 



NA TURE 



303 



The question which is undoubtedly of deepest interest 

 1 this connexion is whether the Charleston earthquake 

 throws any new light upon the origin of such events. 

 While we are not prepared to say that absolutely nothing 

 will be added to our information on this question, we are 

 forced to admit that we expect very little new light. 

 Hitherto our eftbrts have been devoted to bringing to- 

 :4ether the facts and to arranging and comparing them, 

 and we have as yet given but little consideration to this 

 final question. It will, however, shortly engage our 

 ittention, and in anticipation of this we prefer to remain 

 lent for the present, fearing that, if we commit ourselves 

 ere to any preference for a particular view, we may find 

 iirselves encumbered with a bias arising from the in- 

 tensely human propensity to defend, through thick and 

 thin, utterances which have once been formally given. 



ON A POINT OF BIOLOGICAL INTEREST IN 

 THE FLOWERS OF '' P LEU ROTH ALLIS 

 ORNA TUS," RCHB. F. 



T N December of last year (1886), in the Orchid-house at 

 *■ Kew, a specimen of Pleitrothallis ornatus ' flowered. 

 Not only is this the first time that it has done so at Kew, 

 but I am informed by Mr. Watson, of the Royal Gardens, 

 who drew my attention to it, that hitherto P. ornatus has 

 not been known to flower in captivity. 



The flowers of this plant present a most interesting 

 adaptation, whereby to attract insects, of which I propose 

 in this note to give a short account. 



The genus Pleiirothallis is characterized (generally 

 speaking) by the inconspicuousness of its flowers, which, 

 as a rule, are of a reddish-brown colour. The flowers are 

 either solitary and axillary, or in few-flowered racemes. 

 The outer perianth-whorl (sepals), though never exceed- 

 ing a few millimetres in length, is several times longer 

 than the inner (petals). The sepals are sub-equal, and 

 the lateral ones slightly connate at the base. The two 

 lateral petals are small and wing-like on either side of 

 the column. The short, superiorly-grooved labellum is 

 always shorter than the petals, and articulates with the 

 column by a narrow flexible neck. Such an arrange- 

 ment, in consequence of which the labellum is more or 

 less vibratile, and after a touch will oscillate several 

 times, is found in several allied genera, e.g. Restrepia, 

 and especially Bolbophylluw. The genus Pleurothallis 

 is tropical American, and epiphytic. 



Pleurothallis ornatus is especially distinguished from 

 other members of the genus in the fact of its sepals 

 possessing an extremely conspicuous fringe of white 

 cirrhi. In no other species of the genus, of which I have 

 been able to find figures or specimens, is anything of the 

 kind seen.- The hair-like structures which form this 

 fringe in P. ornatus average about 2 millimetres in 

 length ; and when it is remembered that the extreme 

 diameter of an expanded flower does not exceed 10 

 millimetres some idea of the conspicuous part played by 

 the fringe is obtained. Figs, i and 2 are respectively 

 front and lateral views of a flower, magnified about five 

 diameters. Each hair it will be seen narrows very much 

 at its proximal end, and is in this way rendered versatile. 

 From the fact of the hairs being air-containing they are 

 excessively light, and moved by every breath of air. The 

 motion of course is an entirely passive one — they are 

 simply swayed to and fro on the hinge formed by this 

 tapering. 



In Fig. 3 is represented a microscopic view of one of 



' Described by Prof. H. G. Reichenbach in Witlmack's Gartenztitttng, 

 1882, p. 105. To him I am indebted for this reference. 



' Except perhaps in Pleurothallis ciliata, whicli is described and figured 

 by Knowles and Westc >tt in "The Flor.il Album," v^l. i. p. 40. Here, 

 however, it is the petals which have a ciliated border. No description is 

 given of the hairs, though the authors mention having examined them micro- 

 scopically. The figure is a bad one, and barely shows the existence of a 

 fringe. 



the cirrhi detached. It consists simply of a prolongation 

 of one of the epidermal cells at the edge of the sepal — 

 and its lumen is continuous with that of the epidermal 

 cell from which it originates (cf. Fig. 4). In form, the 

 hair resembles that of a flattened club. Its width, through- 

 out most of its extent, averages o'2 millimetres. But it is 

 flattened in the plane at right angles to this, so that its 

 thickness is only about 0*025 millimetres. Externally the 

 hair has a granular aspect, arising from numerous slight 

 rugosities of its delicate cuticle (cf. Fig. 3). At its 

 proximal end it narrows as it runs into the epidermal cell 

 from which it arose. 



In the expanded flower the hairs are air-containing, the 

 protoplasm being entirely collapsed and dried up. 



The versatile hairs are inserted along the margin of 

 the sepals at intervals of less than i millimetre. Towards 

 the attached part of the sepals they become much shorter. 



2 m VI 



Fig. I. — View of the flower from in front, X 5 diameters, c, col imn : z./», 

 petals ; /, labellum ; /.«>./, lateral sepals ; p.o.fi, posterior sepal. 



Fig. 2. — Lateral view of same flower, X 5 diameters. References as iu 

 Fig. I. _ 



Fig. 3. — A single isolated vibratile hair, ranch magn.fied. 



The precise mode of insertion is seen in Fig. 4, which 

 represents a transverse section of the edge of a sepal. 

 The hair is formed from one of a group of small cells 

 {h.c) at the extreme edge of the sepal. In the figure are 

 seen its relations to the parenchyma, and to the upper 

 and lower epidermis {ii.e and l.e) of the sepal. 



I have been unable to examine buds of the plant, con- 

 sequently no account can be given of the development of 

 these hairs. 



As regards its biological meaning, there can, I con- 

 ceive, be little doubt but that the fringe serves to attract 

 insects which fertilize the otherwise inconspicuous flowers. 

 The white lustrous appearance of the cirrhi is a con- 

 sequence of their air-content ; and it is as important a 

 factor as their versatility, in successfully rendering the 

 small brown flowers conspicuous to insects. As I have 



