ABSTRACT
The nature of the viscid matter differs remarkably in different orchids: in Listera it sets hard almost instantly, more quickly than plaster of Paris; in Malaxis and Angraecum it remains fluid for several days; but these two states pass into each other by many gradations. The caudicle, when largely developed and destitute of pollen-grains, is the most striking of the many peculiarities presented by the pollinia. The pollinia of many orchids undergo a movement of depression, after they have been removed from their places of attachment and have been exposed for a few seconds to the air. The long strap-formed disc of Gymnadenia conopsea is well adapted to show the mechanism of the movement of depression. That the power of movement lies exclusively in the surface of the disc is well shown in the case of the saddle-shaped disc of Orchis pyramidalis. The nectar-secreting organs of the Orchideae present great diversities of structure and position in the various genera.
