5 THE ORCHIDS OF NEW ENGLAND. 



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 is 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 is 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. In the course of some hours, or of a day, the rostellum 

 not only slowly recovers its original position (pushing back the 

 pollen-masses, and while this is going on, Muller adds in his 

 account, the groove of the lip is 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 it miserably perished." He 

 also speaks of the number of spider-webs spread over the 

 plants of Listcra ovata, "as if the spiders were aware how 

 attractive the Listera is to insects." 



