Chaf. VI. MOVEMENTS OF THE POLLTNIA. 157 



directly over the stigma, and the movement of the 

 pollinium is always directly downwards. In Calanthe, 

 however, the two stigmas are placed exteriorly to the 

 anther-cells, and the pollinia, as we shall see, are made 

 to strike them by a peculiar mechanical arrangement 

 of the parts. 



In the Ophreae the seat of contraction, which causes 

 the act of depression, is in the upper surface of the 

 viscid disc, close to the point of attachment of the 

 caudicles : in most of the Vandeoe the seat is likewise 

 in the upper surface of the disc, but at the point 

 where the pedicel is united to it, and therefore at a 

 considerable distance from the point of attachment of 

 the true caudicles. The contraction is hygrometric, but 

 to this subject I shall return in the ninth chapter; 

 therefore the movement does not take place until the 

 pollinium has been removed from the rostellum, and 

 the point of union between the disc and pedicel has 

 been exposed for a few seconds or minutes to the air. 

 If, after the contraction and consequent movement of 

 the pedicel, the whole body be placed into water, the 

 pedicel slowly moves back and resumes its former 

 position with respect to the viscid disc. When taken 

 out of water, it again undergoes the movement of de- 

 pression. It is of importance to notice these facts, as 

 we thus get a test by which this movement can be 

 distinguished from certain other movements. 



In Maxillaria ornitJiorhyncha, we have a unique case. 

 The pedicel of the rostellum is much elongated, and 

 is entirely covered by the produced front lip of the 

 anther, and is thus kept damp. When removed it 

 bends quickly backwards on itself, at about its central 

 point, and thus becomes only half as long as it was 

 before. When placed in water it resumes its original 

 straight form. If the pedicel had not been in some 



