FERTILISATIOX. 



79 



" The rostellum has an upper and a small lower surface composed of 

 membrane ; and between these a thick mass of milky white matter is 

 included, which can be very easily forced out. This Avhite matter is 

 less viscid than usual ; when exposed to the air, a film forms over 

 it in less than half a minute, and it soon sets into a waxy or cheesy 

 substance. Beneath the rostellum the large concave but shallow viscid 

 stigmatic surface is seated. The produced anterior lip of the anther 

 {see Fig. A) almost entirely covers the upper surface of the rostellum. 

 The filament of the anther is of considerable length but is hidden in 

 the side view A behind the middle of the anther ; in Fig. B it is 

 seen after it has sprung forward ; it is elastic and presses the anther 

 firmly down on the inclined surface of the clinandrium which lies behind 

 the rostellum. When the flower is expanded the four jioUinia united 



Dendrobiiim chrysanthum. 



A. Lateral Wcw of (lowtT with the anther in its propsr position before the ejection of the pollinia. All 

 the perianth segments are reinoved except the labellum which is longitudinally bisected. 



B. Outline of column viewed laterally after the anther has ejected the pollinia. 



C. Front view nf the column showing the empty cells of the anther after it has ejected its pollinia. The 

 anther is represented hanging too low and covering more of the stigma than it really does. 



", anther ; r, rostellum ; s, stigma ; 1, labellum ; n, nectary. 



into a single mass lie ([uite loose in the clinandrium and under the 

 anther case. The labellum embraces the column, leaving a tubular 

 passage in its front ; the middle portion is thickened as shown in 

 Fig. A ; the thickened portion extends up as far as the top of the 

 stigma. The lower part of the labellum is developed into a saucer-like 

 nectary which secretes lioney. 



"If an insect found its way into one of these flowers, the labellum 

 which is elastic would yield, and the projecting lip of the anther 

 would protect the rostellum from being disturbed ; but when the insect 

 retreats, the lip of the anther will be lifted up and the viscid matter 



