69 THL ORCHIDS OF NilW I NGLAND 
matter (which expels the drop) and the pollen forever locked 
up. Small insects alight on the lip for the sake of the nectar 
copiously secreted (by the furrow on it), as they lick this, they 
slowly crawl up its narrowed surface until their heads stand 
directly beneath the overarching crest of the rostellum; when 
they raise their heads they touch the crest, this then explodes 
(expelling the viscid drop), and the pollen-masses are instantly 
and firmly cemented to their heads. 
“The rostellum, which 1s naturally somewhat arched over the 
stigma, quickly bends forward and downward at the moment of 
the explosion so as then to stand at right angles to the surface 
of the stigma. When the rostellum 1s touched so quickly that 
the pollen-masses are not removed, they become fixed to the 
rostellum and by its movement are likewise drawn a little for- 
ward. Inthe course of some houts, or of a day, the rostellum 
not only slowly recovers its original position (pushing back the 
pollen-masses, and while this 1s going on, Muller adds in his 
account, the groove of the lip 1s secreting fresh honey), but 
becomes quite straight and parallel to the stigmatic surface. 
The downward movement of the rostellum protects the stigmas 
of the young flowers of a plant from impregnation, and the 
upward movement leaves the stigmatic surface of older flowers, 
now rendered more adhesive, perfectly free for pollen to be left on 
it. The pollen-masses, once cemented to an insect’s forehead, will 
remain attached until brought into contact with the stigma of 
a mature flower, then the weak, elastic threads which tie the 
grains together” are ruptured. Sometimes an insect is too 
feeble to remove the pollen-masses, and one was found by Dar- 
win “vainly struggling to escape, with its head cemented by 
the hardened viscid matter to the crest of the rostellum and to 
the tips of the pollen-masses, where 1t miserably perished” He 
also speaks of the number of spider-webs spread over the 
plants of Lestera ovata, “as if the spiders were aware how 
attractive the Listera 1s to insects.” 
