100 NOTES ON THE FERTILISATION 



the large carpenter bees (Xylocopa latipes) sometimes visit 

 the flowers: this is very probably correct for something cer- 

 tainly removes the pollinia occasionally, but nevertheless it 

 cannot be a very common occurrence as I have watched a 

 plant for hours without seeing any insect visitor. On the 

 other hand in the vicinity of this orchid certain trees (a Iaca- 

 randa and a Vitex) which bear blue flow T ers are visited by 

 countless swarms of carpenter bees. These bees every day 

 pass by clumps of Arundina speciosa, Bromheadia palustus 

 and Vanda hookeriana without paying the slightest attention 

 to the orchid flowers. The orchids in question w T ere all grow- 

 ing in cultivated areas and thus to some extent under unnatur- 

 al conditions but the same facts are revealed when we seek the 

 plant at home : for there too the vast majority of flow T ers never 

 set a pod. Nevertheless this does not apply to the small flower- 

 ed orchids : such flowers are generally fertilised and it is quite 

 a usual experience to find a complete spike of seed pods. This 

 is to be attributed probably to the ants which frequent most 

 flowers large or small in numbers : in small flowers an ant is 

 able to remove the pollinia but in large flowers this is not 

 possible. 



In Sarawak the best known orchid is the Dendrobium 

 crumenatum popularly known as the ' pigeon orchid.' It 

 produces conspicuous spikes of sweet smelling white flowers 

 which endure for one day only and then fade away : the spikes 

 appear at irregular intervals of about 50 days. This orchid 

 produces only very few seed pods: nevertheless it is visited 

 by swarms of bees which pass rapidly from flower to flower 

 removing the pollinia from many or all of the flowers on the 

 spike. The pollinia are to be found on the rnetathorax of the 

 bee dorsally. These bees (Apisdorsata) appear early in the 

 morning and by 7 a.m. they crowd round the clumps of pigeon 

 orchid found on almost every tree : by 8.30 a.m. however only 

 few bees are to be seen and at 10 a.m. an occasional straggler 

 is the sole representative of the early morning swarms. By 

 evening (5 p.m.) the flowers have entirely lost their fragrant 

 odour but they are still open and now they receive the atten- 



Jour. Straits Branch 



