HARD WICKE'S SCIENCE-GOSSIP. 



49 



ON MOVEMENTS OF THE POLLINIA OF EXOTIC 



ORCHIDS. 



By J. H. A. HICKS, F.R.H.S. 



HE pollen-granules in 

 orchids are massed 

 together, and kept 

 in that condition 

 by minute highly- 

 elastic threads, 

 which becoming 

 confluent at the 

 base, form the cau- 

 dicle, or supporting 

 stem of the pol- 

 linium. Each pol- 

 linium is protected 

 by, and kept with- 

 in, the anther-case. 

 The caudicle is at- 

 tached to a very 

 small membrane, 

 the pedicel, vari- 

 ously shaped in the 

 different genera ; and on the under side of the 

 pedicel, a gland, or disc, is found, which secretes a 

 viscid fluid. The gland, or disc, is inserted into the 

 rostellum, or superior sterile stigma, which has in 

 some orchid-flowers become so extraordinarily modi- 

 fied, that it is difficult to reconcile it to its primordial 

 condition. 



In flowers of Cattleya crispa, the rostellum is broad 

 and tongue-like, arching over the stigma, and the 

 inferior surface consists of a coating of viscid matter. 

 The pollinia consists of eight waxy clubs of pollen, 

 attached to a confluent bundle of minute elastic 

 fibres, forming the caudicles. The pollen is of two 

 kinds, namely, waxy masses, and distinct compound 

 granules. An insect, after obtaining nectar from 

 the nectary, and in the act of making egress, strikes 

 against the under part of the rostellum, which then 

 turns upward, and the viscid matter being freely 

 No. 339. — March 1893. 



forced up all round, secures the lower end of the 

 caudicles to the retreating insect. Without the aid 

 of insects, or some intruding body, the sticky matter 

 does not come in contact with the free end of the 

 caudicles, and fertilization can therefore not take 

 place. 



In Epidendrium floribundum the upper and lower 

 surfaces, when touched, resolve into a viscid mass ; 

 and the rostellum, with pollinia, is removed as soon 

 as the nectar-seeking insect retreats, or an inserted 

 object is withdrawn. 



Both surfaces of the rostellum of Biilbophylhim 

 coccinum also resolve into sticky matter, and must 

 be forced upwards into the anther by mechanical aid, 

 in order to secure the pollinia. 



The pollen-masses in the Cypripedium section are 

 converted into viscid matter, and the stigmatic sur- 

 face does not exhibit any signs of viscidity, as is usual 

 in many orchids, but is perfectly dry, more or less 

 protuberant and convex, studded with papillse. The 

 pollen-masses possess no caudicles, and there is no 

 rostellum present. Self-fertilization cannot take place, 

 for the fertile anthers are so far removed behind and 

 above the inferior surface of the stigma, that they 

 cannot possibly come in contact with the stigma to 

 effect fertilization ; consequently in a state of nature 

 they are entirely dependent on the removal of their 

 pollen-masses by insect visitors. 



In Dendrobmm chrysanthum the pollen-masses pos- 

 sess no caudicles ; but an insect, in endeavouring to 

 retreat from the nectary, must knock against the lip 

 of the anther projecting over the rostellum ; conse- 

 quently the lip is raised, and the viscid matter of the 

 rostellum spreads into the anther, and the result is 

 the pollen-masses are stuck to and carried away by 

 the insect visitor. 



In Ccelogyne cristata the caudicles of the pollinia 

 are free, and the viscid matter cannot come in con- 



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