REMOVAL OF POLLEN IN ORCHIDS, 257 



ground owing to the stalk-like inferior ovaries being twisted (c/. Plate XIII.). 

 Only quite a few Orchids, oh the other hand, retain the parts of the flower 

 in the same positions, after the bud is open and ready for insects, as were 

 occupied by them in the bud. Epipogium aphyllum, a remarkable plant, which 

 has been already referred to in respect of its peculiar mode of life (see vol. i. 

 p. Ill), may be taken as a type of this group. As shown in fig. 257 ^°, p. 226 of 

 the present volume, five of the perianth-segments of Epipogivmi aphylluTn are 

 long and narrow and slightly incurved. These segments inclose a space in the 

 same sense as the curved fingers of a hollow hand may be said to do so, and in 

 the middle of the space the column presents itself in the shape of a slightly 

 ascending platform for insects to alight on. Arching over it is the sixth leaf 

 of the perianth, the labellum, which resembles a cowl or helmet and causes the 

 whole flower to look somewhat like that of Monkshood. Honey is concealed 

 in the interior of the cowl, and in order to reach it the humble-bees which 

 frequent this Orchid are obliged to crawl up the landing-stage with their bodies 

 in contact with it, that is to say, with the column bearing the stigma and 

 anther. The separate parts of the flower here are in the reversed position as 

 compared with ordinary Orchids, where the labellum is the lowest member. 

 The column bears the anther at its lower extremity, then comes the rostellum, 

 which develops an extremely sticky disc, and still higher up, the steeply-sloping 

 wall of the stigma (see fig. 257 ^^). The oval pollinia are attached to the viscid 

 disc of the rostellum by long ductile filaments or pedicels (see fig. 257 ^'), and are 

 covered over by a membranous hood, the anther-case. When an individual of 

 the species of humble-bee named Bombus lucorum, a frequenter of shady woods, 

 alights on the column of a flower of Epipogium aphyllum and proceeds to 

 crawl from the lower edge of that structure towards the honey concealed in the 

 galeate labellum, it does not at once come into direct contact with the pollinia, 

 they being covered by the hood-like anther-case, but the viscid disc of the 

 rostellum immediately adheres to the under part of the insect's body. After- 

 wards, when the bee leaves the flower, the anther-cap is thrown back and the 

 two pollen-masses attached to the viscid disc are drawn out of their niches and 

 carried away (fig. 257 ^^). The manner of their transference to other flowers will 

 be discussed in the next chapter. 



In many respects similar to these Orchid-mechanisms for promoting a transfer 

 of the pollen are those prevailing in the flowers of Asclepiadacese, where the pollen 

 masses are fastened by special organs of attachment to the feet of insects. Here 

 again the pollen is in the form of pollinia connected together in pairs, and one 

 cannot look at them without being reminded of the analogous structure in Orchids 

 (see fig. 269 *). On nearer inspection, however, important difierences are discovered 

 to exist. In the first place, the little knob ("corpusculum") connecting the two 

 pollinia is not soft and viscid as in Orchids, but is a hard, dry implement with two 

 arms capable of holding any small delicate object by gripping it Kke a clip; 

 secondly, the pollinia are not clavate or of pasty consistency, but are in the form of 



VOL. II. 67 



