EXPULSIVE MECHANISM IN ORCHIDS. 



269 



to one in the stage under consideration, it is repaid for its startling reception in 

 the former case by a rich supply of honey; and in thrusting its pollen -dusted 

 proboscis down to the base of the flower it brings it in contact with the stigma, 

 which stands in the middle of the tube. 



The most noteworthy cases of Orchids furnished with expulsive mechanism 



Fig. 275.— Expulsive app-iratus in Orctiid-flowers : flower of Catasetum tridentatum. 



' Side view. 2 Front view. 8 Longitudinal section tlirougli ttie same; tlie band connecting tlie pollen-masses with the viscid 

 disc is stretched like a bow over the protruding rostellum. < The pollen-masses and viscid disc are liberated and are 

 being jerked away by the sudden straiglitt^ning of the connecting-band; the anther-case which hitherto concealed the 

 pollen-masses tumbles away at the same time (below). ^ Front view of pollen-masses, viscid disc, and tlie band connecting 

 them ; the margins of the baud soniewliat involute. •^ .Side view of the same. ? Column removed from the flower ; towards 

 tlie summit is the anther, below it the elastic connecting-band stretched like a bow ; next the stigmatic chamber with its 

 fleshy margins prolonged into two horn-like irritable processes, s Flower of Deiidrobiuvi fimbriatum, 9 Tlie same in 

 longitudinal section, ^o Side view of the hood-like antlier at the end of the column. 11 The anther jerking back and 

 ejecting the pollen-masses. 1- Pollen-masses of Dendrobiuvi Jlmbriatum. i"^ ", 12 x 5; the rest natural size 



are those of the genera Catasetum and Dendrobium. Catasetum will need a some- 

 what detailed account, for the reason that in this genus the process of expulsion 

 ensues upon an external stimulus which does not act upon the mechanism in 

 question direct, but is transmitted through a special organ. The column in the 

 flower of Catasetum (see figs 275' and 275-), as in many other Orchids, rises 



