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216 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 pollinium 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 pollinium, 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 antennæ 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 Catasetum, 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 pollinium, when ejected, formed a hoop round it with the viscid surface outside; if I used a broad flat object, the pollinium struggled against it and sometimes coiled itself 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