2094 



A TEXTBOOK OF THEORETICAL BOTANY 



whorl, the third is represented by a large staminode placed posterior to the 

 anthers and more or less covering the stigma. All three stigma lobes are 

 functional, the pollen is granular and not united into masses or distinct 

 pollinia. This group therefore represents those members in which the 

 normal monocotyledonous flower is least modified. 



I. Cypripedieae. Flowers with well-marked median symmetry and two 

 fertile stamens, the anterior stamen forming a large staminode. 

 The ovary is unilocular or trilocular. 



Included in this tribe is the single genus Cypripedium (Fig. 2030) con- 

 taining about thirty species, which by some are separated into several genera. 

 The plants are widely distributed in north temperate zones and in the 

 tropics of Asia and America. The South American species, in which the 



Fig. 2030. — Cypripedium flower. A cultivated 

 variety. 



ovary is trilocular, are often separated into the genus SeJenipediiim. The only 

 British representative is C. calceoliis, the Lady's Slipper Orchid, now 

 limited in this country to the woods around Durham and north Yorkshire. 

 The so-called slipper is made up of the labellum which plays an important 

 part in the pollination mechanism. In this species (Fig. 2031), the labellum 

 is yellow in colour while the rest of the flower is purple. This colour together 

 with the scent of the nectar attracts small bees, which creep into the 

 inflated labellum, and find there juicy hairs which may secrete nectar. 

 There are three openings which serve as entrances to the cavity of the 

 labellum; two lateral ones, on either side of the column, and a median 

 large opening in front of it. Insects invariably choose this latter entrance. 



