796 



LECTURE XLV. 



The adaptations for cross-pollination in most Orcliids, as various as they are 

 complicated and ingenious, have been described in detail by Darwin in the book cited 

 above One of the simpler, and, in its main features, commoner cases is presented by 

 Epipactis latifolia, and may be here shortly described. At the time when the sexual 

 organs are mature, the flower, in consequence of a twisting of the pedicel, stands so 

 that what is properly the posterior of the six perianth-leaves hangs forwards and 

 downwards ; its basal portion is deepened like a bowl and thus transformed into a 

 receptacle for the nectar which it produces itself (Fig. 454 B, D, I). , The sexual 

 apparatus, borne by the Gynostemium 5 (in C) projects obliquely over this 



nectary; the stigma forms a disk with several 

 lobes and is deepened and viscid in the centre, 

 its surface being bent obliquely over the de- 

 pression of the labellum. Right and left, above,' 

 to the sides and behind the stigma, are situated 

 the two aborted glandular stamens xx; above 

 the stigma, hanging over like a roof, is the 

 single fertile anther, which is rather large and 

 is in its turn roofed over by its cushion-like 

 connective {en). The side-walls of the two 

 halves of the anther spring open longitudinally 

 to the right and left, so that the pollen-masses 

 are partially freed; the pollen-grains are con- 

 nected together by means of a viscid material. 

 In the middle in front of the anther and above 

 the stigmatic surface is found the so-called ros- 

 tellum h, a peculiarly metamorphosed portion 

 of the body of the stigma (cf. A); the tissue 

 of the rostellum is converted into a viscid sub- 

 stance which is covered only by a thin mem- 

 brane. The flower of Epipactis left to itself 

 does not get fertilised, for the pollen-masses 

 do not spontaneously fall out of the anthers, and 

 even if they did would not come on to the 

 stigmatic surface: they must be removed by 

 insects and transferred to the stigma of another 

 flower. The manner in which this is accom- 

 plished may be rendered clear with the aid of 

 a sharp-pointed lead-pencil. On pushing the 

 point under the stigmatic surface in the direction of the base of the labellum, and 

 then pressing it a little on the rostellum, and again withdrawing it slowly, in the 

 same position [D), the viscid mass of the rostellum — the adhesive-disc — remains 

 sticking to the pencil, with the adherent pollen-masses. These latter are now 

 completely extracted from the two anther-halves on the withdrawal of the pencil, 

 as shown in E and F. If the pencil-point together with the poUinia are again 

 pushed into another flower in the direction of the base of the labellum, the pollinia 

 necessarily come in contact with the viscid portion of the stigmatic surface and stick 



Fig. ^e^^— Epipactis latifolia {an Orchid). A 

 longitudinal section of a flower-bud. B newly-opened 

 Bower after removal of the perianth except the label- 

 lum I. C sexual apparatus after the removal of all the 

 perianth-lobes — seen from in front and below. D as 

 B : the point of a pencil is inserted after the manner 

 of the proboscis of an insect ; E and i^ pencil-point 

 witl\ pollinia attached. fK ovary ;/ labellum, the bag- 

 lilce depression of which functions as a nectary; n the 

 broad stigma ; *n the connective of the one fertile 

 anther ;/ pollinia ; A the rostellum 'y xxt\i6 two abor- 

 tive lateral gland-like stamens; i' insertion of the 

 - excised labellum. 5 (in Q the gynostemium. 



