THE MOXOCOTYLEDOXES 



21 II 



Owing to the shape of the chnandrum and the elasticity of the stamen 

 filament, the pollinium always springs forward over the rostellum as soon 

 as the anther is lifted up by a visiting insect. In this way it remains hanging 

 over the stigmatic surface. Should the insect fail to remove the pollinium 

 it seems probable that as the labellum springs back at the insect's emergence, 

 the movement is sufficient to shake the pollinium on to the stigma and thus 

 effect self-pollination. 



This elasticity of the filament occurs only in a few species of Dendrobium, 

 as far as is known, but in at least one species it has been observed that flower 

 buds which failed to open have later produced fertile capsules, which sug- 

 gests that some form of self-pollination must have occurred. 



Hamtnarhxa pahidosa (Fig. 2050) is the only representative of this genus. 

 It is widely distributed in north temperate regions including, as we have 



Fig. 2050. — Hammarbya (Malaxis) paludoso. A, Flower, drawn in the normal 

 orchid position with the labellum downwards. In nature the flower is 

 twisted through 360 so that the labellum is upwards. B, The two pollinia. 

 C, Back view of the mature column with the shrivelled remains of the 

 anther exposing the two pollinia. The chnandrum forms a shield around 

 them. (A after Rendle. B and C after Dancin.) 



mentioned, Britain. The flowers are peculiar in that the ovary is twisted 

 through 360° so that the labellum becomes once again uppermost. The 

 flowers are very small but on examination are found to possess a central 

 column which is more or less triangular. As seen from below two lateral 

 portions of the clinandrum flank and enclose the rostellum, while below is 

 the pocket-like stigmatic surface formed from a fold of the column tissue. 

 Viewed from the back the two anthers lie side by side on the back of the 

 rostellum. As they mature the anthers shrivel leaving the two pollinia 

 exposed. Each pollinium consists of a pair of very thin plates of waxy 



