EXPULSIVE MECHANISM IN ORCHIDS. 



209 



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 apparatus in Orchid-flowers : flower of Catasetum tridentatum. 



1 Side view. 2 Front view. 3 Longitudinal section through the same ; the band connecting the pollen-masses with tlie viscid 

 disc is stretclied like a bow over the protruding rostellum. ■* The pollen-masses and viscid disc are liberated and are 

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

 pollen-masses tumbles away at the same time (below). 6 Front view of pollen-masses, viscid disc, and the band connecting 

 them ; the margins of the band somewhat involute. ^ Side view of the same. ' Column removed from the flower ; towards 

 the 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. ^ Flower of Dendrobium fi.mbriatum. 9 The same in 

 longitudinal section, lo Side view of the hood-like anther at the end of the column, n The anther jerking back and 

 ejecting tlie pollen-masses, i- Pollen-masses of Dendrobium fimbriatum. i", u, 12 x 5; the rest natural size 



are those of the genera Catasetum and Dendrohiuni. 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 meclianism in 

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

 flower of Catasetum (see figs. 275^ and 275 2), as in many other Orchids, rises 



