216 VANDEiE. Chap. Vn. 



mentary summit of the column no doubt having been 

 thus disturbed. When I gently prised up the anther- 

 case at its base or on one side, the poUinium was 

 ejected, but then the sensitive hinge would necessarily 

 have been bent. When the flower has long remained 

 expanded and is nearly ready for spontaneous ejection, 

 a slight jar on any part of the flower causes the 

 action. Pressure on the thin pedicel of the poUinium, 

 and therefore on the underlying protuberant rostellum, 

 is followed by the ejection of the pollen-masses ; but 

 this is not surprising, as the stimulus from a touch 

 on the sensitive hinge has to be conveyed through 

 this part of the rostellum to the disc. In Catasetum 

 slight pressure on this point does not cause the act 

 of ejection ; but in this genus the protuberant part of 

 the rostellum does not lie in the course along which 

 the stimulus has to be conveyed from the antennae 

 to the disc. A drop of chloroform, of spirits of wine, or 

 of boiling water placed on this part of the rostellum 

 produced no effect ; nor, to my surprise, did exposure 

 of the whole flower to vapour of chloroform. 



Seeing that this part of the rostellum was sensitive 

 to pressure, and that the flower was widely open on 

 one side, and being pre-occupied with the case of Cata- 

 setum, I at first felt convinced that insects entered the 

 lower part of the flower and touched the rostellum. 

 Accordingly I pressed the rostellum with variously- 

 shaped objects, but the viscid disc never once adhered 

 in a proper manner to the object. If I used a thick 

 needle, the poUinium, when ejected, formed a hoop 

 round it with the viscid surface outside ; if I used a 

 broad flat object, the poUinium struggled against it 

 and sometimes coiled itseU up spirally, but the disc 

 either did not adhere at all, or very imperfectly. At 

 the close of the twelfth trial I was in despair. The 



