Ciur. IX. GRADATION OF ORGANS. 249 



secure the pollen-masses, but indirectly by means of 

 their attachment to an insect's body. 



The viscid matter of the rostellum and of the 

 stigma appear to have nearly the same nature ; that 

 of the rostellum generally has the peculiar property of 

 qiiickly drying or setting hard ; that of the stigma, 

 when removed from the plant, apparently dries more 

 quickly than gum- water of about equal density or 

 tenacity. This tendency to dry is the more remarkable, 

 as Gartner * found that drops of the stigmatic secre- 

 tion from Nicotiana did not dry in two months. The 

 viscid matter of the rostellum in many Orchids when 

 exposed to the air changes colour with remarkable 

 quickness, and becomes brownish-purple ; and I have 

 noticed a similar but slower change of colour in the 

 viscid secretion of the stigmas of some Orchids, as of 

 Gephalaniliera grandijlora. When the viscid disc of an 

 Orchis, as Bauer and Brown have observed, is placed 

 in water, minute particles are expelled with violence 

 in a peculiar manner ; and I have observed exactly 

 the same fact in the layer of viscid matter covering 

 the stigmatic utriculi in an unopened flower of Mor- 

 modes ignea. 



In order to compare the minute structure of the 

 rostellum and stigma, I examined young flower-buds 

 of Epideiidrum cochleatum a.nd florihundum, which, when 

 mature, have a simple rostellum. The posterior parts 

 of both organs were quite similar. The whole of 

 the rostellum at this early age consisted of a mass 

 of nearly orbicular cells, containing spheres of brown 

 matter, which resolve themselves into the viscid fluid. 

 Tlie stigma was covered with a thinner layer of similar 

 cells, and beneath them were the coherent spindle- 



BeitraRR zur Keniitnias dcr Befrucl.tung,' 1S44, p. 2:HG. 

 12 



