350 ANGIOSPERMAE—DICOTYLEDONES 



LXXXIX. ORDER CYTINACEAE BROGN. 



769. Brugmansia Blume. 



2486. B. Zippelii Blume. — 



Visitors. — Delpino says (' Ult. oss.') that this species is pollinated by flesh-flies, 

 which are kept prisoners for some time in the flowers. Darwin, on the other hand, 

 considers that the pollinators are long-beaked humming-birds, while short-beaked 

 ones steal nectar by perforation. 



770. Rafflesia R.Br. 



2487. R. Arnold! R.Br.; 2488. R. Horsfieldii R.Br.; and 2489. R. Patma 

 Blume. — 



Visitors. — Delpino supposes (' Ult. oss.') that these species are pollinated by 

 carrion-flies. 



XC. ORDER ARISTOLOCHIACEAE JUSS. 

 771. Aristolochia Toum. 



Species of this genus bear protogynous pitfall-flowers, usually secreting a little 

 nectar (perhaps by the edges of the trap). 



2490. A. clematitis L. (Sprengel, ' Entd. Geh.,' pp. 418-29 ; Hildebrand, 

 Jahrb. wiss. Bot., Leipzig, v, 1874; Delpino, 'Ult. oss.,' pp. 228-9 ; Herm. Miiller, 

 'Fertilisation,' p. 517; Correns, Jahrb. wiss. Bot., Leipzig, xxii, 1891, pp. 161-89, 

 Bot. Centralbl., Cassel, lii, 1892, pp. 439-43.) — Sprengel discovered the working of 

 the flower mechanism in this species by his acute investigations, overlooking only the 

 protogyny of the flowers and their consequent cross-polUnation, which characteristics 

 were subsequently found out by Hildebrand. Correns turned his attention to the 

 anatomy and physiology of the hairs which close the entrance to the pitfall. 



The flower is bright yellow, the middle part of its perianth formmg a tube, 

 which widens below into a globular trap, and is produced above into a tolerably fiat 

 limb. When this last unfolds the flower is upright, and the tube is beset with down- 

 wardly-directed hairs on the inner side, which allow tiny insects (flies and gnats) to 

 enter, but prevent them from creeping out again. During this stage the stigma is 

 receptive, but the six gynandrous anthers are still unripe. In the vain attempt to find 

 nectar or obtain their freedom once more, the insects, if the\' have brought pollen 

 from another flower, will dust the stigma with it, and effect cross-pollination. The 

 anthers then dehisce, and the hitherto upright flower-stalk begins at the same time to 

 bend downwards, while the hairs closing the flower-entrance shrivel, so that the exit 

 is no longer barred to the little prisoners. Completely covered with pollen, thev 

 emerge and transfer it to a flower in the first stage. Finally the limb of the perianth 

 drops so far down that the tube of the flower (now^ completel}' reversed in position) 

 is completely closed, and no longer accessible to insects. 



Corren says that the weel-hairs temporarily closing the entrance to the trap grow 

 more and more thickly as they approach it, but scarcely increase in size. He also 



