PLATE V. 



Eeproductions of photographs of the flower of Dendrobium Dalhousieanum 

 Paxt., with the petal and sepal on one side removed, also half of the lip and of the 

 dorsal sepal. The nectary has not been opened. For three of these photographs 

 I used a dead specimen of the common English honey-bee, which is approxi- 

 mately the size of Lithurgus atratus, the bee which fertilizes this orchid in 

 N. Siam. The photographs are slightly smaller than life size. The flowers were 

 very kindly supplied by Messrs. Sander, of St. Albans. 



Pig. 1. — Normal position of anther. 



Fig. 2. — A bee, after entering the passage, has just commenced to retreat. 

 The anther is very slightly tilted. 



Fig. 8. — The bee has retreated clear of the passage, but is not yet free of 

 the anther, which is now considerably tilted. The pollinia 

 have been drawn from their cells, and can be seen adherent 

 to the thorax of the bee. 



Fig. 4. — A bee attempting to enter after the dislocation of the anther. 



