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A TEXTBOOK OF THEORETICAL BOTANY 



fertile and contain pollen mixed with a glutinous fluid. The stigma is convex 

 and stands below the staminode, in the tube formed by the labellum. Its sur- 

 face is not sticky, but is rough with papillae which can scrape the glutinous 

 pollen from an insect. Flies and small bees {Andrena) enter the pouch and 

 cannot crawl out of it directly, but have to go up the tubular part, where they 

 meet, first the stigma, then the two fertile anthers. Thus they leave on the 

 stigma any pollen they may be carrying and emerge at the base of the labellar 

 tube smeared with fresh pollen. 



The flowers of Coryanthes (Fig. 1250) are pendulous and the distal part 

 of the labellum forms a large " bucket ", turned inwards adaxially. Two 



appendages at the base of the label- 

 lum hang over this bucket and secrete 

 fluid in a steady flow of drops into the 

 bucket, which may contain as much 

 as 30 c.c. at a time. The fluid is only 

 faintly sweet and is not the main attrac- 

 tion, for bees come to gnaw the tissue 

 of the labellum itself. The bucket 

 is provided with a spout turned to- 

 wards the column and fitting closely 

 to it, with the poUinia and stigmas 

 immediately above the spout. The 

 bees are small species of Eiiglossa and 

 they come in such numbers that they 

 jostle one another into the bucket. 

 The first to fall in wallows his way 

 through the water to the spout and 

 in pushing his way out carries off the 

 pollinia. Subsequent victims may 

 bring pollen with them, which they 

 leave on the stigma, since the same 

 insect may be repeatedly immersed. 

 Darwin remarked about this extra- 

 ordinary performance that it "ap- 

 peared utterly incredible !" 



Fig. 1250. — Coryanthes speciosa. Pendu- 

 lous flower with distal part of labellum 

 forming large " bucket ". The exit 

 spout is turned to the left. {After 

 Daruin.) 



[c) Pitfall Inflorescences 



The type of pitfall mechanism developed in Arum inaculatum is more 

 elaborate and involves the trapping of the flies in a prison formed around an 

 inflorescence. In this type the insects move from the region of the axis 

 on which female flowers are produced, to one in which there are male 

 flowers. Both their passage from the one to the other and their final escape 

 are delayed by downward-projecting hairs which wither progressively, 

 so that when they do finally escape the flies are completely smothered 

 with pollen. Miiller suggests that this climax type may have been evolved 

 from forms like Calla palustris or Lysichiton in which the spathe surrounds, 



