80 AEETHUSE^ Chap. IIL 



CHAPTEK IIL 



AEETHUSE^. 



Cephalanthera grandiflora ; rostellum aborted ; early penetration of the 

 pollen-tubes; case of imperfect self-fertilisation ; cross-fertilisation 

 effected by insect^i which gnaw the labellum — Cephalanthera ensi- 

 folia — Pogonia— Pterostylis and other Austialian orchids with the 

 labellum sensitive to a touch — Vanilla— Sobraha. 



Cephalanthera grandiflora, — This Orchid is remark- 

 able from not possessing a rostellum, which is so 

 eminently characteristic of the order. The stigma is 

 large, and the anther stands above it. The pollen 

 is extremely friable and readily adheres to any object. 

 The grains are tied together by a few weak elastic 

 threads ; but they are not cemented together, so as to 

 form compound pollen-grains, as in almost all other 

 Orchids.* In this latter character and in the complete 

 abortion of the rostellum we have evidence of degrada- 

 tion ; and Cej)halanthera appears to me like a degraded 

 Epipactis, a member of the Neottese, to be described in 

 the next chapter. 



The anther opens whilst the flower is in bud and 

 partly expels the pollen, which stands in two nearly 

 free upright pillars, each nearly divided longitudinally 

 into halves. These subdivided pillars rest against or 

 even overhang the upper square edge of the stigma, 

 which rises to about one- third of their height (see front 



♦ This separation of the grains by Lindley in hi's magnificent 

 was ob.served, and is represented, ' Illustrations of Orchidaceous 

 by Bauer in the plate published Plants.' 



