24 



NATIVE BRITISH ORCHIDACE^ 



PL B, fi^. 2, illustrates the pollination of Anacamptis pjramidalis, the Pyramid 

 Orchid.' A^^shows the 5-lobed column above the lip, with the 2-celled anther in the 

 longer upper lobe, and the pollinia showing through the fissure in the front of each 

 cell. At its foot is the rostellum, r, a pouch containing the viscidium, shown m C 

 andD, to which the pollinia are attached so firmly that they stand erect. On the oval 

 surface of each side-lobe of the column is one of the two stigmas, s, s, which are 

 quite separate. At the base of the 3-lobed lip are two guiding plates, /', /', which 

 appear in the figure to be flat. They really stand erect at right angles to the Up, and 

 converge towards the rostellum where they nearly meet. 



As might be imagined from the long spur, the flowers are visited by butterflies 

 and moths— Darwin enumerated 23 visiting species— and the poUinia are invariably 

 attached to the proboscis. As this organ is very slender and thread-like, and repeatedly 

 curled and uncurled like a watch spring, the ordinary rounded disc-like viscidium 

 oWrMs, which answers admirably for attachment to a flat surface, would be insuffi- 

 cient to secure a firm hold on a thin mobile proboscis. The viscidium is therefore 

 strap-like— Darwin called it saddle-shaped— and the two ends curl round the moth's 

 proboscis on withdrawal, just meeting round it, and grasping it firmly. As the viscid 

 matter beneath it rapidly sets hard like cement, there can be no turning round side- 

 ways, and the hold is firm and rigid. Darwin found that if the pollinia were with- 

 drawn by their caudicles, the ends of the strap, having nothing to grasp (?l. B, 

 fig. 2, D), curled inwards till they touched each other in nine seconds, and m nine 

 more'closed up into an apparently solid ball.' A naturaUst, who sent him a moth 

 with several viscidia attached to its proboscis, remarked that the moth had cleverly 

 bored through the exact centres of the sticky glands of some orchid. 



As in Orchis, the poUinia after withdrawal move downwards through an angle 

 of nearly 90°, so that they then lie in the same plane as the needle or proboscis, 

 F and G. The curling movement of the viscidium incidentally brings about a beautiful 

 adjustment. The two pollinia originally stand erect and nearly parallel. If they remained 

 parallel after the downward movement when attached to a proboscis, on insertion 

 into another flower they would be too close together, and would be pushed agamst 

 the rostellum, which would be useless. But the curling movement of the viscidium 

 makes them diverge a little, so that they come in contact with the two lateral stigmas, 

 and leave packets of pollen adhering to them. 



It is essential that the insect's proboscis should touch the under-surface of the 

 viscidium exactly in the middle, or the pollinia would be attached crookedly. As the 

 entrance of the spur is spacious compared with a moth's proboscis, the rostellum is 

 placed lower down in the mouth of the spur than in Orchis, and restricts the entrance 

 to a narrow passage. To secure the necessary accuracy a special device, found m no 



• Darwin, Feri. Orch. ed. 2, p. 21. 



