288 FEETILISATION EFFECTED BT MEANS OF INSECTS. 



at the bottom of the tube, fertilises the pistil with the pollen which 

 it has carried with it from another flower. This plant is proto- 

 gynous, the stigma being matured before the stamens. When the 

 flower is duly fertilised it sinks down, no longer presenting a tempting 

 orifice for the entrance of insects. If no insect visits the chamber, 

 then the stigma passes its maturity before the pollen of its own flower 

 is ripened, and no fertilisation takes place. 



Orchids with very long nectaries, such as Anacamptis, Gymna- 

 denia, and Platanthera, are habitually fertilised by Lepidoptera, while 

 those with only moderately long nectaries are fertilised by bees and 

 Diptera. The length of the nectary is correlated with that of the pro- 

 boscis of the insect which visits the plant. Orchis Morio has been 

 seen fertilised by the hive-bee (Apis meUifica), to some of which 10 

 or 16 poUen-masses were attached; by Bombus muscorum, with 

 several poUinia attached to t'he bare surface close above the mandibles ; 

 by Eucera longicomis, with 1 1 poUinia attached to the head, and by 

 Osmia rufa. Empis livida has been seen fertilising Orchis maculata. , 



In Listera (fig. 317, p. 205) the viscid mass of the rostellum bursts 

 with force, and then allows the poUinia to escape. The nectar in 

 some species of Orchids is secreted between the outer and inner mem- 

 brane of the nectary, and bees puncture the inner lining of the 

 nectary and suck the fluid contained between the coats. In some 

 Orchids, as in Neotinea intaota, there is evident self-fertilisation, 

 although there is also provision for fertilisation by insects. So also in 

 Ophrys apifera, Gymnadenia, Platanthera, Epipactus, Cephalanthera, 

 Neottia, Epidendrum, Dendrobium. In Disa grandiflora the weight 

 of the pollen masses bends the caudicle. In this plant the posterior 

 sepal secretes nectar. In Ooryanthes, Gongora, Catasetum, Stan- 

 hopea, etc., the extraordinary crests and projections on the labeUum 

 are gnawed by insects, and while doing so they are sure to touch the 

 viscid disk of the poUinia and remove them. The flowers of these 

 plants exhibit remarkable animal forms, probably with the view of 

 attracting insects. It has been remarked that in Orchids the forms 

 of the perianth resemble those of the insects belonging to the native 

 country of the plant. The flowers also secrete a large amount of 

 saccharine matter, and are odoriferous ; their pollen masses are very 

 easUy detached, and are very adhesive. AU these circumstances seem 

 to be connected with their mode of impregnation. In Asclepiadacese, 

 which have also peculiar pollinia (fig. 386, p. 230), insects are 

 attracted by the odour of the flowers (sometimes very fetid, as in 

 Stapelia), as well as by saccharine matter. 



Darwin states that bees always alight on the left wing petal (ala) 

 of the scarlet kidney-bean, and in doing so depress it ; and this acts 

 on the tubular and spiral keel petal (carina), which causes the pistil 

 to protrude. On the pistil there is a brush of hairs, and by the 



