ORCHIDEAE 



407 



like a helmet, directed upwards, and secretes nectar on its inner side. The five 

 other downwardly directed perianth leaves are long, narrow, and slightly bent 

 upwards, thus enclosing a space, in the middle of which the column consisting 

 of stigma and anther is situated ; this slopes gently upwards and forms an alighting- 

 platform. Kerner states that humble-bees probing for nectar touch this platform 

 with the under-side of their bodies in climbing upwards over it. On the downwardly 

 directed end of the column are situated first the anther, next the rostellum, with very 

 sticky papillae, and finally, 

 still higher up, the stigma, 

 forming a steep wall. The 

 ovoid poUinia are united 

 to the sticky papillae of 

 the rostellum by long, 

 tough threads, and covered 

 by a membranous cap 

 belonging to the anther. 

 The wood humble-bee 

 (Bombus lucorum Z.) 

 found in shady woods, 

 uses the column as an 

 alighting - platform, and 

 from its lower edge probes 

 for nectar in the galeate 

 labellum ; it does not 

 immediately come into 

 contact with the concealed 

 poUinia, but the sticky 

 papillae of the rostellum 

 adhere to the under-side 

 of its body. When the 

 insect leaves the flower, 

 the cap covering the pol- 

 linia springs back, so that 



the two pollinia clinging to the disks are torn out and carried away. At the same 

 time they turn over, so that they now hang downwards from their caudicles like two 

 cherries on their stalks. The whole of the structure thus torn out elongates somewhat, 

 so that the pollinia can be deposited on the stigma of another flower. The stigma is 

 situated above the rostellum, and if the pollinia did not possess long caudicles, 

 they could not be pressed on it by humble-bee visitors. 



Rohrbach, who has described the flower-mechanism very minutely, states that 

 the spur and the upper margin of the labellum serve as an alighting-platform for the 

 insect, whence it creeps on to the labellum round its tip. It then reaches the down- 

 wardly directed perianth leaves, raises it head, and clings comfortably to the labellum, 

 with the intention of emptying the nectary, and bores into the inner surface of this to 

 suck out the juice. When leaving the flower, the insect must climb down the down- 

 wardly directed column, and thus strikes against the rostellum, causing its epidermis 



Fig. 376. Herminium. Monorckis, R. Br. (after Herm. Mttller). 

 A. Flower, seen from the side. B. Do., from the front, with the perianth 

 leaves forcibly separated. D. Do., in the natural position, seen from 

 the side (X 7). D. Pollinia. E. Reproductive organs and base of 

 labellum (x 32). a a, anther-lobes; a' a', vestigial anthers; br, bract; 

 kl kl, disks; ov, ovary; pp, lateral petals; p', labellum; ss, lateral 

 sepals; *', upper sepal ; sp, spur; */, stigma: xx, recesses below disks; the 

 arrows in B indicate lateral accesses to spur. 



