lOo NATIVE BRITISH ORCHIDACE^ 



it is so near the underside of the rostellum that it is sure to touch its sensitive surface. 

 It should be noted that tlie lip narrows gradually upwards, so that the insect is 

 infallibly led to the exact position in which it must touch the rostellum. Immediately 

 it does so the miniature explosion takes place, and the startled insect flies off, carrying 

 the polHnia to another plant. If he now alights on a flower from which the poUinia 

 have already been taken, the trail of honey will lead him right to the base of the lip, 

 where the pollinia on his head will come in contact with the sticky stigma, to wliich 

 little masses of pollen will adhere, as the pollen-grains are only fastened to the pollmia 

 by weak easily broken threads. 



Nor are the delicate mechanical adjustments even now exhausted. When the anther 

 has deposited the stalkless pollinia on the back of the rostellum, the latter curves a 

 little downwards, to avoid the tip of the anther being caught by the viscid drop, and 

 thus glued to the rostellum, locking up the pollinia for ever. The rostellum also bends 

 quickly downwards at the moment of the explosion— an additional precaution against 

 the above danger. In its new position it also tends to keep off poUinia-bearing insects 

 from the stigma, which does not mature quite so early as the pollinia. In the course 

 of some hours after, the rostellum slowly rises until it is well out of reach of any 

 insect crawling up the Up, leaving the way to the stigma clear. An insect arrivmg 

 with pollinia is therefore no longer checked by toucliing the rostellum, but goes on 

 to the base of the lip, when the pollinia come in contact with the stigma, whose 

 sticky surface, by this time mature, is able to detach and retain httle masses of pollen. 

 These disintegrate into tetrads, and these again into single grains, which emit pollen- 

 tubes in the usual way, the latter penetrating the ovary and fertihsing the ovules. 



Sprengel several times saw Iclineumon flies withdraw the pollinia.' One stayed 

 long on a flower, and, on holding another flower near it, crawled to it, sucked the 

 nectar, and on reacliing the bend of the lip, touched the rostellum. Immediately 

 the pollinia became affixed to its head. He also saw a small beetle carrying poUinia. 

 One sunny afternoon in May, 1867, Hermann MuUer watched about 20 plants 

 simultaneously, and often on each tliree or more insects were busy sucking honey. 

 He concentrated his attention on a single insect, and did not catch it until it had 

 accomplished at least one act of pollination, and in most cases three or four. One 

 specimen of Grammoptera Icevis was already laden with pollinia when he first saw it. 

 It visited six flowers, carrying off pollinia from four, and leaving pollen on the stigmas 

 of two, which had already lost their own pollinia. Judging from the number of 

 hardened discs on its head, it must have already fertilised many flowers before he 

 began to watch it.^ Spiders appear to have observed how attractive the flowers are 

 to insects, for their webs are frequently found on Listera ovata. 



The marvellous co-ordination of parts in this exquisite and comphcated piece of 

 I Das entdeckte Geheimniss der Natur (179})- ' MuUer, Fert. ofFlomrs, p. 530. 



