go ANGIOSPERMAE—DICOTYLEDONES 



LXVII. ORDER ASCLEPIADEAE R.BR. 



In the sub-order Cynanchoideae the five filaments are broadened, generally 

 fused into a tube, and provided with external appendages which make up a corona ; 

 anthers usually with terminal membranous appendages; pollen aggregated into 

 poUinia, attached in pairs to the clip-glands of the large capitate stigma. The clips 

 grasp the legs of insect-visitors when the nectar-secreting spots are on the same radii 

 as the stamens (Asclepias), or the proboscis if these spots alternate with the stamens 

 (Vincetoxicum, Stapelia, Bucerosia, Araujia). The clips are thus drawn out of their 

 recesses by the legs or proboscis of visitors, and transferred to other flowers. 

 (Pinch-trap flowers.) The extremely specialized flower mechanisms are adapted 

 to insect visitors in a very perfect manner, so that a comparison may be made with 

 orchids, though in this case there is nothing like the same variety. 



According to K. Schumann (' Asclepiadaceae,' in Engler and Prantl's ' D. nat. 

 Pflanzenfam.,' IV, 2), the flower mechanism of the sub-order Periplocoideae exhibits 

 an undoubted analogy to that of the Ophryoideae. 



568. Vincetoxiciun Rupp. 



Yellowish-white pinch-trap flowers, arranged in axillary stalked umbels, and 

 pollinated by means of the proboscis of insect visitors. 



1874. V. officinale Moench (= Asclepias Vincetoxicum Z., and Cynanchum 

 Vincetoxicum Pers.). (Sprengel, 'Entd. Geh.,' pp. 139-50; Delpino, ' Ult. oss.,' 

 pp. 224-8; Hildebrand, Bot. Ztg., Leipzig, xxviii, 1870, pp. 604-5 j Herm. Miiller, 

 'Alpenblumen,' pp. 350-2; Kirchner, 'Flora v. Stuttgart,' p. 546.) — The flowers of 

 this species smell of honey. The ovaries are surrounded by a fleshy column 

 formed by fusion of the stamens, and covered by a fleshy disk, under which are 

 five entrances to the stigmas. The staminal column bears the five anthers at 

 its end, and also, externally, five appendages (cuculli) fused together to form 

 a domed corona. The anthers are closely apposed to the terminal knob of the 

 style, and each of them contains a pair of plate-like pollinia lodged in loculi 

 opening on the side turned inwards. The connective is produced into a triangular 

 membranous appendage which is closely applied to the top of the stylar knob. 

 Each side of the anther is continued into a leaf-like wing, narrowing gradually 

 above and vertical to the column of filaments. The adjoining wings of every 

 two anthers bound between them a narrow slit that widens below. These slits 

 open internally into a stigmatic chamber, which is partly bounded by the stigmatic 

 surface on the under-side of the terminal expansion of the style. Lying in the 

 upper part of each slit, and visible externally, is a dark, bilaterally symmetrical 

 shining body (corpusculum), consisting of a hard, thin, horny plate. Its sides 

 are bent forwards for their whole length so that their edges lie close together, 

 and in the middle of its lower border there is a wedge-shaped slit. Two 

 pollinia, lying in the adjacent loculi of two different anthers, are attached by 

 bands to this ' clip.' 



If now a fly tries to suck the nectar contained in one of the coronal pits, 

 situated immediately below a clip, its extended proboscis, beset with erect bristles, 

 will be guided upwards in the slit between the adjacent anther-wings until it is 



