INFLUENCE OF THE ORIGIN OF THE CELLS ON FERTILISATION. 



913 



collects below and behind the stigma among the hairs of the channel. An insect 

 which has already brought pollen on its proboscis from another flower inserts its pro- 

 boscis beneath the stigma through the channel into the nectary. The foreign pollen, 

 which is attached to the proboscis, is thus rubbed off on to the lip of the stigma, it is de- 

 tained by the viscid secretion which fills up the hollow of the latter, and subsequently 

 emits its pollen-tubes through the canal of the style. While the insect is sucking 

 the nectar in the spur, the pollen of this flower, which lies in the channel behind the 

 stigma, becomes attached to the proboscis; when the proboscis is again drawn out, 

 this pollen does not come into contact with the viscid stigma, the lip being drawn 

 forward by the motion of the proboscis, and the orifice of the stigma protected. The 

 pollen that is removed from this flower is now carried, in the manner described, to 

 the stigma of another flower. If the insect were to insert its proboscis again into the 

 nectary of the same flower, the pollen would be detached into the cavity of its own 



Fig. 492. — Epipactis latifolia: A longitudinal section through a flower-bud; B open flower after removal 

 of the perianth with the exception of the labellum/; C the reproductive organs after removal of the perianth 

 seen from below and in front ; D as &', the point of a lead-pencil b inserted after the manner of the proboscis of 

 an insect; /J' and F the lead-pencil with the pollinia attached; yA' ovary, / labellum, its bag-like depression 

 serving as a nectary, n the broad stigma, en the connective of the single fertile anther, / pollinia, h the rostellum, 

 XX the two lateral gland-like staminodes, i place where the labellum has been cut oflf, s the gynostemium. 



stigma ; but, as Hildebrand has remarked, insects do not usually do this, but suck up 

 the nectar only once, and then visit another flower. The proceedings of the insect 

 may be imitated by inserting a fine sharp pin beneath the stigma into the channel 

 and again withdrawing it, and filling with the pollen thus removed the stigmatic 

 cavity of another flower. 



The contrivances for cross-pollination in Orchids, as numerous as they are compli- 

 cated and ingenious, have been described in d&tail by Darwin in the work already 

 named ^ One of the simpler cases, and the most frequent in its main features, may be 

 briefly described in the case of Epipactis latijolia. At the time when the reproductive 

 organs are mature, the flower stands, in consequence of a torsion of its pedicel, so that 

 the true posterior leaf of the six that form the perianth (the labellum) hangs in front and 



* See also Wolff, Beitriige zur Entwickelungsgeschichte der Orchideen-bllithe, in Jahib. ftir wiss. 

 Bot. vol. IV, 1865. 



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