80 GENERAL REVIEW OF THE ORCHIDEJ;, 



of the rostellum will be forced into the anther, gluing the pollen 

 masses to the insect whicli will transport it to another flower. If 

 this action he imitated artificially, l)y inserting the point of a pencil 

 for instance, then owing to the inclination of the base of the 

 clinandriuni and to the length and elasticity of tlie filament, Avhen 

 the anther is lifted up it is always sliot over the rostellum and 

 remains hanging there, with its lower empty surface suspended over 

 the summit of the stigma (Fig. C). The filament now stretches across 

 the space which was originally covered by the anther {see Fig. B). If 

 after having cut off all the perianth segments, the flower be laid under 

 the microscope, and the lip of the anther be raised by a needle without 

 disturbing the rostellum, the anther may l)e seen to assume, with a 

 spring, the position represented sideways in Fig. B, and frontways in 

 Fig. C. By this springing action, the anther scoops the pollen mass 

 out of the concave clinandriuni and pitches it up in the air with exactly 

 the right force so as to fall down on the middle of the viscid stigma 

 where it sticks. 



" Under nature, however, the action cannot be as thus described, for 

 the labellum hangs downwards, and to understand what follows the 

 drawing should be placed in an almost reversed position (nearly upside 

 down). If an insect failed to remove the pollinia by means of the 

 viscid matter from the rostellum, the pollinia would first be jerked 

 downwards on to the protuberant surface of the labellum placed im- 

 mediately beneath the stigma. But it must be remembered that the 

 labellum is elastic, and that at the same instant that the insect in 

 tlie act of leaving the flower lifted up the lid of the anther and so 

 caused the pollen masses to be shot out, the labellum would rebound 

 back and striking the pollen masses would pitch them upwards so as 

 to hit the sticky stigma. 



" This view of the use of the elastic filament, seeing how complicated 



the action must be, may appear fanciful ; but we have seen so many 



and such curious adaptations that one cannot believe the strong elasticity 



of the filament and the thickening of the middle of the labellum to 



be useless points of structure. If the action be as above described, 



it might be an advantage to the plant that its pollen masses should 



not be wasted if they failed to adhere to an insect by means of the 



viscid matter from the rostellum." * This contrivance is not common 



to all the species of Dendrobium. 



The time that elapses from the pollination of the flower to the 



fertilisation of the ovules and thence to the maturing of the seed 



capsules varies considerably in the different genera and even in 



species belonging to the same genus. It was one of the discoveries 



* Fertilisation of Orchids, pp. 172 — 177. In the text Mr. Darwin uses the words pollinium 

 and pollen mass as if this species had but one, but it really has four like all other species of 

 Dendrobium. 



