Ohap. IV. LISTEKA OVATA. 123 



generally in large quantity, on all the stigmas which 

 I examined. 



I will recapitulate the several special adaptations 

 for the fertilisation of this plant. The anther-cells 

 open early, leaving the pollen-masses free, protected 

 by the summit of the column, and with their tips 

 resting on the concave crest of the rostellum. The 

 rostellum then slowly curves over the stigmatic 

 surface, so that its explosive crest stands at a little 

 distance from the summit of the anther ; and this 

 is very necessary, otherwise the summit would 'be 

 caught by the viscid matter, and the pollen for ever 

 locked up. The curvature of the rostellum over the 

 stigma and over the base of the labellum is excellently 

 adapted to favour an insect striking the crest when it 

 raises its ■ head, after having crawled up the labellum 

 and licked the last drop of nectar. The labellum, as 

 C. K. Sprengel has remarked, becomes narrower where 

 it joins the column beneath the rostellum, so that 

 there is no risk of an insect going too much to either 

 side. The crest of the rostellum is so exquisitely 

 sensitive, that a touch from a very minute insect 

 causes it to rupture at two points, and instantly two 

 drops of viscid fluid are expelled, which coalesce. This 

 viscid fluid sets hard in so wonderfully rapid a manner 

 that it rarely fails to cement the tips of the poUinia, 

 nicely laid on the crest of the rostellum, to the fore- 

 head of the touching insect. As soon as the rostellum 

 has exploded it suddenly curves downwards so as to 

 project at right angles over the stigma, protecting it 

 from impregnation at an early age, in the same manner 

 as the stigmas of the young flowers of Spiranthes are 

 protected by the labellum clasping the column. But 

 as the column of Spiranthes after a time moves from 

 the labellum, leaving a free passage for the introduc- 



