ASCLEPIADEAE 



93 



1875. V. medium Decne. (=V. latifolium C. Koch). — 



Visitors. — Plateau saw the hover-fly Melanostoma mellina L. in the Ghent 

 Botanic Garden. 



1876. V. purpurascens C. Morr. et Decne. — 



Visitors. — Plateau saw the house-fly Musca domestica L. in the Ghent 

 Botanic Garden. 



569. Asclepias L. 



Pinch-trap flowers. Pollination eff'ected by the legs of insects. 



1877. A. syriaca L. (= A. Cornuti Decne.). (Delpino, ' Sugli appar. d. fecondaz. 

 nelle piante autocarp.,' pp. 6-15; Hildebrand, Bot. Ztg., Leipzig, xxiv, 1866, p. 376, 

 XXV, 1867, pp. 265, 273, 281 ; J. P. Mansel Weale, J. Linn. Soc, Bot., London, xiii, 

 1873, pp. 48-58 ; Herm. Mijller, ' Fertilisation,' pp. 396-400, ' Weit. Beob.,'III, p. 61 ; 

 T. H. Corry, Trans. Linn. Soc, Bot., London, Ser. 2, ii, 1884, pp. 173-207, Proc. 

 Phil. Soc, Cambridge, iv, 1883, pp. 5-6 ; Stadler, 'Beitrage.') — Hildebrand has given 

 the rnost exhaustive account of the way in which this species is pollinated by insects, 

 while Hermann MuUer was the first to publish drawings of the flower mechanism 

 (Fig. 255), which agrees essentially with that of Vincetoxicum officinale. 



Fig. 256. AscUpias syriaca, Decne. (from K. Schumann, after Payer). A. Flower seen from the side : 

 ca, calyx ; «?, corolla. B, Do., after removal of calyx and corolla, visited hy a wasp, to the feet of which 

 some poUinia are attached. C. Longitudinal section of flower: n, corolla; anth, anthers; /r, ovary; 

 Kfl, stigmatic disk ; st, stamens. 



But while the latter is a pinch-trap flower adapted to nectar-seeking flies, to 

 the proboscis bristles of which its minute clips become attached, Asclepias syriaca 

 bears flowers of a kind adapted to bees, the claws of which become entangled in 

 the clips and carry off the pollinia to be introduced into the stigmatic chambers 

 of other blossoms. As before, an odour of honey is exhaled. The petaloid 

 appendages (cuculli) of the anthers are in the form of five fleshy nectar-pockets, 

 which alternate with the clips. From the bottom of each of these arises a curved 

 horn-shaped process that bends inwards over the stigmatic disk. 



An insect searching for nectar slips about on the smooth flowers which make 

 up the umbel until one of its feet gets a firm hold in the lower part of a slit. When 

 it wishes to go on, and draws up the leg, the claws are guided upwards in the slit so 

 that the clip becomes attached to the foot During subsequent movements the 



