914 PHENOMENA OF SEXUAL REPRODUCTION. 



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

 for the nectar which it secretes (Fig. 492, 5, 73, /). The sexual organs, borne on the 

 gynostemium 5 (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 x x 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 ^, a peculiarly 

 metamorphosed part of the stigma (see ^) ; 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 

 slightly against the rostellum, and again withdrawn slowly in this position (D), the viscid 

 mass of the rostellum or adhesive disc of the pollinia to which the pollen-masses are 

 attached remains sticking to the pencil. The pollinia are now completely removed from 

 the two anther-lobes by the withdrawing of the pencil, as is shown in E and F. If the 

 pencil with its pollinia attached is now again inserted into another flower in the direction 

 of the bottom of the labellum, the pollinia necessarily come into contact with the viscid 

 stigmatic surface and adhere firmly to it ; when the pencil is again withdrawn they are 

 left behind, being partially or entirely torn from the pencil. In consequence of the form 

 and position of the parts of the flower, an insect which settles on the anterior part of the 

 labellum would in the same manner be able to creep into the bottom of the nectary with- 

 out disturbing the rostellum ; but when it again crept out after obtaining the nectar, it 

 would strike against it and carry off" the pollinia ; and on crawling into a second flower, 

 these would come into contact with the viscid stigma, and would remain attached to it. 

 In some other Orchidese the contrivances are much more complicated. 



(3) The ripe pollen has often to remain for a considerable time in the open anthers, 

 in the case of flowers in which pollination is eff'ected by insects, before it is carried 

 away. During this time it might be blown away by the wind or wetted by rain or dew. 

 In order to prevent this, numerous and very different contrivances exist which protect 

 the pollen. For details see Kerner, Die Schutzmittel des Pollens (Innsbruck, 1873). 



Sect, 34. — Hybridisation \ In the preceding paragraphs we have spoken 

 only of the union of the reproductive cells of the same plant, or of two individuals of 

 the same species. We learn however from experience that a fertile sexual union can 

 take place between plants which are specifically distinct. A union of this kind is 

 called Hybridisation^ and its product a Hybrid. According as the union takes place 

 between different varieties of one species, diff'erent species of one genus, or between 



* J. G, Kolreuter, Vorlaufige Nachricht von einigen das Geschlecht der Pflanzen betreffenden 

 Versuchen u. Beobachtungen, Leipzig 1761; Appendices in 1763, 1764, and 1766. — W. Herbert, 

 On Amaryllidacese, with a treatise on cross-bred vegetables; London, 1837. — Gartner, Versuche vi. 

 Beobachtungen liber die Bastarderzeugung im Pflanzenreich ; Stuttgart, 1 849. [See notice by 

 Berkeley, Journ. Roy. Hort. Soc. vol. V, 1850, p. 156,] — Wichura, Die Bastardbefruchtung im 

 Pflanzenreich, erlautert an den Bastarden der Weiden (with two nature-printed plates) ; Breslau, 

 1865. [See abstract by Berkeley, Journ. Roy. Hort. Soc. new series, vol. I, 1850, p. 57. — Focke, 

 Pflanzen Mischlinge, 1881.] 



