202 THE BOOK OF NATURE STUDY 



As looked at from in front one of the three leaves of the outer 

 whorl stands in the middle line behind, while the other two stand 

 to either side of the flower. The three leaves of the inner whorl 

 alternate with those of the outer whorl. Two, standing towards 

 the back of the flower, are small and narrow, like the leaves of the 

 outer whorl, and their tips bend inwards so as to meet. They 

 form, together with one of the leaves of the outer whorl, a hood- 

 like structure overarching and protecting the parts within. The 

 third leaf of the inner whorl is very different in shape and size to 

 the others. It forms a wide apron-shaped lip to the front of 

 the flower (Fig. 92, 3), and is continued back as a tubular spur 

 (Fig. 92, 2). It is called the lip or labellum. 



The parts of the flower within the perianth may be seen on 

 looking into the flower (Fig. 92, 3), or by removing all the perianth- 

 leaves from a flower (Fig. 92, 5). Looking into the opening above 

 the labellum which leads into the spur, the back wall of the open- 

 ing appears to be formed by two dull white surfaces, which are 

 continuous across the middle line and have their edges defined 

 by a coloured line. These areas are the two receptive lobes of 

 the stigma. Immediately above the stigma is the single stamen, 

 which is not very like in appearance to the stamens of most 

 flowers. The two anther lobes are shaped like Indian clubs 

 with their dilated ends pointing upwards (Fig. 92, 3). They lie 

 parallel to one another, and their narrower ends come in contact 

 with a small globular structure overhanging the entrance to the 

 spur. This is known as the rostellum, and corresponds to the 

 third lobe of the stigma specially modified to perform a particular 

 function. 



The anther lobes have a purple colour, but when opened by 

 a longitudinal slit the greenish mass of pollen is visible in each. 

 This is not as usual loose and powdery, but all the pollen of each 

 anther lobe is joined together to form a club-shaped mass or 

 pollinium. The lower part of this forms a tapering stalk which 

 is connected to the membrane forming the back of the rostellum. 

 The rostellum when mature consists of a thin membranous wall 

 enclosing a sticky substance, which has resulted from the breaking 

 down of the central tissue. The sticky material has collected 

 in two little hemispherical masses against the parts of the mem- 



