108 NEOTTEiE. Chap. IV. 



is endowed with a remarkable kind of irritability ; 

 for, if the furrow be touched yery gently by a needle, 

 or if a bristle be laid along the furrow, it instantly 

 splits along its whole length, and a little milky 

 adhesive fluid exudes. This action is not mechanical, 

 or due to simple yiolence. The fissure runs up the 

 whole length of the rostellum, from the stigma beneath 

 to the summit : at the summit the fissure bifurcates, 

 and runs down the back of the rostellum on each side 

 and round the stern of the boat-formed disc. Hence 

 after this splitting action the boat-formed disc lies 

 quite free, but embedded in a fork in the rostellum. 

 The act of splitting apparently never takes place 

 spontaneously. I covered a plant with a net, and after 

 five of the flowers had fuUy expanded they were kept 

 protected for a week : I then examined their rostella, 

 and not one had split ; whereas almost every flower 

 on the surrounding and uncovered spikes, which would 

 almost certainly have been visited and touched by 

 insects, had their rostella fissured, though they had 

 been open for only twenty-four hours. Exposm-e for 

 two minutes to the vapour of a little chloroform causes 

 the rostellum to split ; and this we shall hereafter see 

 is likewise the case with some other Orchids. 



When a bristle is laid for two or three seconds in the 

 furrow of the rostellum, and the membrane has con- 

 sequently become fissured, the viscid matter within 

 the boat-formed disc, which lies close to the surface 

 and indeed slightly exudes, is almost sure to glue the 

 disc longitudinally to the bristle, and both are with- 

 drawn together. When the disc, with the pollinia 

 attached to it, is withdrawn, the two sides of the ros- 

 tellum (fig. D), which have been described by some 

 botanists as two distinct foliaceous projections, are left 

 sticking up like a fork. This is the comrnon con- 



