EARLY SUMMER FLOWERS 203 



brane to which the stalks of the pollinia join on the outside. 

 These two circular discs of the membranous wall of the rostellum 

 are defined by a split which forms in the membrane when the 

 flower is mature. Anything that presses against the front of 

 the rostellum will press down that part of the membrane and 

 expose the two sticky discs. These will adhere to the object 

 touching them, and carry away with them the pollinia from the 

 anther lobes. 



Touching the front of the rostellum with the point of a pencil 

 will show the general structure and remove one or both of the 

 club-shaped pollinia (Fig. 92, 4, 6), which can then be examined 

 with a lens. In each we distinguish the little patch of membrane 

 at the base, the stalk, and the mass of pollen grains held together 

 in packets by sticky threads. 



To either side of the single fertile stamen a small whitish 

 projection will be seen on careful inspection (Fig. 92, 5). Each of 

 these is the last remains of a stamen, and they mark the position 

 of two other stamens in the flower, though these no longer form 

 pollen. If (having recognised the single stamen, the two rudi- 

 mentary stamens and the stigma, one lobe of which forms the 

 rostellum) the relative positions of these parts are considered in 

 a flower from which all the perianth-leaves have been removed, 

 they will be found to be joined together. The stamens appear 

 to be joined to the back of the style (Fig. 92, 5), or more 

 correctly the stamens and the stigma are carried up together, 

 forming a region known as the column. 



If we now return to the intact flower we shall be in a position 

 to understand how the various parts of this complicated mechan- 

 ism work together in pollination. In the first place, it is obvious 

 that if a flower is left undisturbed there will be no likelihood 

 of self -fertilisation taking place. The flower is completely 

 dependent on insect visits for pollination. Bees and flies visit 

 the flower for a sweet juice, which is not as in most Orchids 

 accumulated in the spur, but is obtained by probing the soft 

 walls of this. The insect alights on the labellum, and in inserting 

 its head into the opening of the tube comes in contact with the 

 rostellum. It depresses the lower part of this, and so exposes the 

 viscid discs. These adhere to the head or proboscis of the insect, 



