ARISTOLOCHIACEAE 



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The flowers of Aristolochia are adapted to pollination 

 by insects, especially by small flies, which are attracted by 

 the dull colour of the flowers and the fetid smell which 

 most of them emit. The flowers are protogynous, the 



Fig. 82 b. Aristolochia Petersiana Klotzsch. A. Branch with a leaf and two flowers. 3/4. 

 B. Flower in longitudinal section. 3/2. C. The ovary and gynostegium. 3/1. 

 From specimens collected in East Africa. 



stigma being receptive while the anthers are still closed. 

 Flies which have entered a freshly opened flower are 

 barred from leaving it at once by various contrivances. 

 In some species, as in the often cultivated European 

 A. Clematitis, the upper and narrow part of the perianth- 

 tube is guarded by reversed bristles which point inwards, so 

 that until these bristles shrivel the insects will not be able 

 to escape. The shrivelling, however, takes place only after 

 the anther-cells have opened and the pollen becomes 

 exposed ; hence the escaping flies, coming in contact with 

 the anthers, necessarily carry away some of the pollen 

 and deposit it on the receptive stigma of another flower 

 in an earlier stage. 



