Chap. II. TERISTYLUS VIRIDIS. (Vo 



classification can be correct. Tlie rostella are small 

 and widely separated from each other. The viscid 

 matter on the under side oi the disc forms an oval ball 

 Avhich is enclosed Avithin a small pouch. The upper 

 membrane to which the caudicle is attached is of large 

 size relatively to the whole disc, and is freely exposed 

 to the air. Hence probably it is that the pollinia when 

 removed from their cases do not become depressed 

 until, as Mr. T. H. Farrer has observed, twenty or 

 thirty minutes have elapsed. Owing to this long 

 interval, I formerly thought that they did not undergo 

 any movement of depression. Supposing a pollinium 

 to be attached to the head of an insect, and to have 

 become dej)ressed, it will stand at the proper angle, 

 vertically, for striking the stigma. But from the 

 lateral position of the anther-cells, notwithstanding 

 that they converge a little towards their upper ends, 

 it is difficult at first to see how the pollinia when 

 removed by insects are afterwards placed on the 

 stio-ma ; for this is of small size and is situated in the 

 middle of the flower between the two widely separated 

 rostella. 



The explanation is, I believe, as follows. The base 

 of the elongated labellum forms a rather deep hollow 

 in front of the stigma, and in this hollow, but some way 

 in advance of the stigma, a minute slit-like orifice (n) 

 leads into a short bilobed nectary. Hence an insect, 

 in order to suck the nectar with which the nectary is 

 filled, would have to bend down its head in front of 

 the stigma. The labellum has a medial ridge, which 

 would probably induce an insect first to alight on 

 eitiier side ; but, apparently to make sure of this, 

 besides the true nectary, there are two spots (n'n') which 

 secrete drops of nectar on each side at the base of 

 the labellum, bordered by prominent edges, directly 



