118 NEOTTEiE. Chap. IV. 



seconds the whole drop sets hard, soon assuming a 

 purplish-brown tint. So exquisitely sensitive is the 

 rostellum, that a touch from the thinnest human hair 

 suffices to cause the explosion. It will take place 

 under water. Exposure to the vapour of chloroform 

 for about one minute also caused an explosion; but 

 the vapour of sulphuric ether did not thus act, though 

 one flower was exposed for, five, and another for 

 twenty minutes to a strong dose. The rostellum of 

 these two flowers when afterwards touched exploded in 

 the usual manner, so that sensitiveness had not been 

 lost in either case. The viscid fluid when pressed 

 between two plates of glass before it has set hard is 

 seen to be structureless ; but it has a reticulated 

 appearance, perhaps caused by the presence of glo- 

 bules of a denser immersed in a thinner fluid. As the 

 pointed tips of the poUinia lie on the crest of the 

 rostellum, they are always caught by the exploded 

 drop : I have never seen this once to fail. So rapid 

 is the explosion and so viscid the fluid, that it is 

 difficult to touch the rostellum with a needle, however 

 quickly this may be done, without removing the 

 poUinia. Hence, if a bunch of flowers be carried 

 home in the hand, some of the sepals or petals will 

 almost certainly touch the rostellum and withdraw the 

 poUinia ; and this gives the false appearance of their 

 having been ejected to a distance. 



After the anther-cells have opened and the naked 

 pollinia have been left resting on the concave back of 

 the rostellum, this latter organ curves a little forwards, 

 and perhaps the anther also moves a little backwards. 

 This movement is of much importance ; if it did not 

 occur, the tip of the anther, within which the pollinia 

 are lodged, would be caught by the exploded viscid' 

 matter, and the pollinia would be for ever locked up 



