INFLUENCE OF THE ORIGIN OF CELLS ON FERTILISATION. 815 



the inferior petal in which the nectar collects, secreted by the appendages of the two 

 inferior stamens. The only entrance to this nectary, which therefore lies behind the 

 reproductive organs, is through a deep channel in the inferior petal, lined with hairs. 

 The upper and lateral petals incline towards one another in front of the ovary which 

 is surrounded by the anthers, and above the channel in such a manner that the entrance 

 to it is entirely filled up by the capitate stigma B, n. The stigma is seated on a flexible 

 style (Cfgr), is hollow and opens by an orifice which faces the hairy channel of the 

 lower petal ; the lower and posterior margin of this orifice has a lip-like appendage. 

 The anthers open of their own accord, and the pollen in the form of a yellow powder 

 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 (see also Fig. 364, p. 499). 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 poflen does not come into contact wuth 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 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 proceeding 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 detail 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 latifolia. 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 

 downward ; it is hollowed out in its lower part, and is thus transformed into a receptacle 

 for the nectar which it secretes (Fig. 461, B, D, /). The sexual organs, borne on the 

 gynostemium S (in C) project obliquely above this nectary; the stigma forms a disc 

 with several lips hollowed out and viscid in the centre, the surface of which is in- 

 clined obliquely above the nectary. The two gland-like staminodes xx stand right 

 and left beside the stigma ; above the stigma and covering it like a roof lies the 

 single fertile anther, of considerable size, which is again on its part protected above 

 by its cushion-like connective en; the lateral walls of the two anther-lobes burst 

 lengthwise right and left, so that their pollen-masses (pollinia) became partially exposed, 

 the pollen-grains remaining attached to one another by a viscid substance. In front of 

 the middle of the anther and above the stigmatic surface is the rostellum >6, a peculiarly 

 metamorphosed part of the stigma (see yi) ; the tissue of the rostellum is transformed 

 into a viscid substance covered only by a thin membrane. The flower of Epipactis is 

 not fertilised if left to itself ; the pollinia do not fall of their own accord out of the 

 anther, and would even then not reach the stigmatic surface ; they must be carried away 

 by insects to the stigma of other flowers. The mode in which this is eff'ected is ex- 

 plained by inserting the point of a black-lead pencil into the flower in a direction towards 

 the bottom of the labellum and beneath the stigmatic surface ; if it is then pressed 



^ See also Wolff, Beitriige zur Entwickelungsgeschichte cler Orchideen-bliilhe, in Jahib. fiir \vi 

 • vol. IV, 1865. 



