Feb. 2 2, 1877] 



NATURE 



357 



REMARKABLE PLANTS » 



II.— Some Curious Orchids. 



I . f^ENERA L Structure of the Flower of Orchids. — The 

 ^-^ exotic representatives of the natural order Orchideae 

 have long been favourite objects of cultivation in our 

 hot-houses, from the beautilul and often bizarre form 

 assumed by their curious flowers. Great as is the variety 

 in the size, colour> and form of the flower in the different 

 genera, it is, nevertheless, more than in most natural 

 orders, constructed al^vays on one plan in its main 

 features. Before describing some of the more remark- 

 able forms, it will be necessary to give a general descrip- 

 tion of this type, and to define the more important of the 

 technical terms used by botanists in relation to it. Both 

 in this account and in the description which follows of 

 particular species, we are largely indebted to Mr. 

 Darwin's most interesting work ^ on orchids, of which a 

 new edition has just appeared ; the illustrations are also 

 reproduced, by the kindness of the publisher, from the 

 same work. 



In all orchids the number of sepals and petals (which 

 together form the perianth) is three each, the former being 

 almost always nearly or quite as brightly coloured as the 

 latter. One of the petals— really the upper one, but, in 

 consequence of the twisting of the ovary, apparently the 

 lower one — is nearly always larger than the others, and 

 is so situated as to form a convenient stage for insects to 

 settle on. It is called the lower lip or labellum (Fig. i, /.), 

 and often assumes the most singular and fantastic shapes. 

 It secretes nectar or honey, which is often contained in a 

 longer or shorter spur-shaped prolongation or nectary («) 

 at its back, but sometimes in the tissue itself, which is then 

 commonly gnawed by insects. There is only one fertile 

 stamen (rarely two), which is confluent with the stigma, and 

 forms with it the column. The anther {a) consists of two 

 cells, which are usually very distinct, and often so widely 

 separated as to appear like two anthers. The pollen is 

 not, in most orchids, in the form of a fine granular pow- 

 der, but coherent into two club-shaped masses, the pollen- 

 masses or pollinia ( p), one contained in each anther-cell ; 

 these are prolonged below into a kind of stalk termed the 

 caudicle {c). The ovary is inferior (beneath the calyx), 

 often presenting the appearance of a stalk to the flower, 

 and consists of three carpels closely united together into 

 a single cavity. The single stigma {s) is sessile upon the 

 ovary, and is confluent with the stamen i^gyitandrous). 

 Its upper part is modified into an extraordinary organ 

 called the rostellum (r), which, when mature, consists 

 partly or entirely of viscid matter. In many species the 

 pollinia are firmly attached to a portion of the exterior 

 membrane of the stigma, which, when insects visit the 

 flower, is removed, together with the pollinia. This 

 removable portion of the rostellum is called the viscid 

 disc {d), or by some authors the "gland" or "re- 

 tinaculum " ; when large, the portion to which the pol- 

 linia is attached is called the pedicel (often confounded 

 with the caudicle). The part of the rostellum which is 

 left after the removal of the disc and viscid matter is 

 called the fovea, or sometimes the " pouch " or " bur- 

 sicula." In the present paper we propose to give an 

 account of a few orchids, interesting from the remarkable 

 mode in which fertilisation by insects is effected. 



2. Coryanthes macrantha. — The genus Coryanthes be- 

 longs to the tribe Vandese, which includes many of the 

 most magnificent extra- British orchids. The extraor- 

 dinary mode of fertilisation is certified by Dr. Criiger, 

 director of the Botanic Gardens at Trinidad. The ac- 

 companying figure (Fig. 2) represents the flower of C. 

 speciosa, an allied species, but will serve to show the rela- 

 tive position of the parts. It is very large, and hangs 



' Continued from p. 299. 



• "The Various Contrivances by which Orchids are Fertilised by Insects." 

 By C larles Darwin, M.A., F.R.S., &c., Second^ Edition, revised, with 

 Illustrations. (Londoa : J. Murray, 1S77.) 



downwards. The lower portion of the labellum (l) is 

 converted into a kind of bucket (b). Two short ap- 

 pendages (h), which arise from the narrowed base of the 

 labellum, stand directly over this bucket, and secrete so 

 much limpid and slightly sweet fluid that it drops into 

 the bucket ; the quantity secreted by a single flower is 

 said to be about an ounce, but it does not appear to 

 attract insects. When the bucket is full, this fluid 

 overflows at a channel which forms a kind of spout (p), 

 closely over-arched by the end of the column, which bears 

 the stigma and pollinia in such a position that an insect, 

 forcing its way out of the bucket through this passage, 

 would first brush with its back against the stigma, and 

 afterwards against the viscid discs of the pollinia, and 

 thus remove them. In C. macrantha the labellum is, 



Fig. I.— Orchis 7nascula. A, side view of flower, with greater part of perianth 

 cut away ; b, front view of flower ; c, poUinium and viscid disc ; D, 

 caudicles with the viscid discs lying within the rostellum ; E, section 

 through rostellum. ; f, packets of pollen-grains ; <i, anther ; r, rostellum ; 

 s, stigma ; /, labellum ; n, nectary ; p, pollinium ; c, caudicle of pol- 

 linium ; d, viscid disc. 



according to Dr. Criiger,^ provided with crests, which are 

 gnawed by bees, as is commonly the case with the label- 

 lum of the Vandese. In this case the bees have been 

 determined by Mr. F. Smith, of the British Museum, to 

 belong to the genus Euglossa. Dr. Criiger states that 

 these bees may be seen in great numbers disputing with 

 each other for a place on the edge of the " hypochil " or 

 basal part of the labellum. Partly by this contest, partly, 

 perhaps, intoxicated by their food, they fall into the 

 bucket, which is half full of the fluid already mentioned. 

 They then crawl along in the water towards the anterior 

 side of the bucket, where they arrive at the spout. But, 

 in order to extricate itself through this opening, the bee 

 has to use considerable exertion, as the mouth of the 



' Journal 0/ Linnean Society, Botany, vol. viii., 1864, p. 130. 



