384 



HUTCHINSON'S POPULAR BOTANY 



pand, exposing the stigmatic surface, and the flower is cross-pollinated 

 by insect agency. 



The Common Birthwort (Ariatolochia clematitis) is a remarkable 

 instance of a protogynous flower. Fig. 461 shows a section through the 

 swollen base of the dull yellow perianth, in the interior of which we see 

 the six-lobed stigma and a few of the anther-lobes, which are sessile on the 

 short style. Now the stigma of this Birthwort matures two or three days 

 before the anthers are ripe, and at the time of its maturity the flower 

 is entered by small black midges of the genera Ceratopogon and Chironomus. 

 It will be noticed that the dull yellow corolla of the flower is swollen at the 

 base, but contracts above into a tube which is lined, in the first stage 



of the flower, with stiff downward- 

 pointing hairs. Along this tube the 

 midges crawl in quest of refresh- 

 ment, which they find in the succu- 

 lent tissue that forms the smooth 

 walls of the roomier chamber below. 

 From the centre of the floor of this 

 chamber uprise the six short sta- 

 mens, the anther-lobes of which are 

 adnate to the stigmatic column. 

 Their meal finished, the midges 

 rest awhile, soothed by the warmth 

 of the apartment. Then they turn 

 to depart. But egress is a different 

 thing from ingress, and on crawling 

 to the tube they find that escape 

 is cut off. The hairs which they 

 had passed over so easily are now 

 a stockade of bristling points. The 

 little guests are prisoners ! 



What is to be done ? At first 

 the midges take the calamity with calmness, and explore their prison with 

 evident care. In the course of their explorations they crawl over the stigmatic 

 surface and supposing them to have come from another flower fertilize 

 the ripe stigma with the pollen which they have brought thither. Hours pass 

 away : the stigma withers ; but the midges are still held captive. A whole 

 day goes by two days and release seems as far off as ever. They become 

 anxious and restless. On the third day the anthers open and discharge 

 their pollen, and the midges, worked up by this time into a fine bustle 

 of alarm, get repowdered with the yellow meal. Their term of imprison- 

 ment is now at an end, for lo ! the prison bars have collapsed the stockade 

 of hairs has completely withered, and the midges pass easily out of the 

 flower, laden with an abundant freight ! 



FIG. 473. TIGER-STRIPED ONCID (Oncidium 

 tigrinum). An Orchid 



