50 



fall, but in a very short time assume a stony hardness which 

 is a striking phase in their life history. 



At this stage the disc and stipites are found to have 

 undergone complete separation from the rostellum, the former 

 being merely retained in position by its sticky under-surface. 

 A touch on the disc now easily removes the whole pollinarium, 

 and the pollinia undergo "^'the act of depression" within one 

 minute of its removal. This ''act of depression" is brought 

 about by the curving downwards of two stipites to which the 

 pollen-masses are attached. The pollinarium rapidly becomes 

 hard, and the disc is firmly cemented to the object removing 

 it. The substance fastening the pollinia to the stipites is, 

 however, very elastic, and does not become dry like the other 

 parts, so that the whole apparatus may remain effective, even 

 when it has been attached for a long time to the head of a 

 visiting insect. 



If the pollinarium be now presented to the stigma, it will 

 be found that the pollinia are so spaced as to fit exactly into 

 the little cup-like depressions already noticed in the ends of 

 the stigmatic cavity (fig. 6). Here they adhere, and any 

 attempt to withdraw the pollinarium results in the separation 

 of the masses from the stipites and their retention in the 

 stigma, the disc and stipites being carried away by the object 

 first responsible for their removal. 



The lahellum (figs. 7 and 8) is about half an inch long, 

 i.e., twice the length of the column. The long middle lobe is 

 keeled from the tip to a point a little below its centre, which 

 marks its contact with the base of the bevelled portion of the 

 column (fig. 9). Here it gives place to two raised lines with 

 a tuft of hairs between them forming a pad. The tip is fur- 

 nished with a woolly landing place, the hairy condition being 

 traceable for some distance along the keel, thus forming a good 

 walking track. The hairs point inwards towards the stigma. 

 The lateral lobes are half the length of the middle one. They 

 are smooth and petaloid, and clasp the column on each side 

 of the stigma. 



As already stated, a wedge-shaped space (fig. 9) contain- 

 ing the stigma is enclosed between the bevelled portion of the 

 column and the labellum. Facilities are afforded a visiting 

 insect to enter this space — a good landing place, an easy foot- 

 ing until it is reached. The presence of the insect is, how- 

 ever, strictly limited to this part of the flower, where its opera- 

 tions will be useful. It cannot proceed further down the 

 column, because of the close contact of the latter with the 

 labellum and the presence of the hairy pad. It is prevented 

 from straying to the sides by the lateral lobes of the labellum. 

 On entering it will not remove the pollinarium, because it 



