GEITONOGAMY 



41 



III. Geitonogamy. 



Kerner, in his paper ' Die Schutzmittel der Bliite,' was the first to distinguish 

 between Geitonogamy and Xenogamy. According to the few experiments of Darwin 

 (' The Effects of Cross- and Self-fertilisation ') and of Hildebrand (' Geschlechter- 

 verteilung,' pp. 67, 68) it appears, as was to be expected, to be less advantageous 

 for the plant than Xenogamy, but considerably more advantageous than Autogamy. 

 Geitonogamy is brought about not only by atmospheric currents and the agency of 

 insects, but also by mature stigmas coming into contact with the pollen-covered anthers 

 of neighbouring flowers, or by the fall of pollen. Kerner gives a full account of these 

 two latter kinds of Geitonogamy in his ' Nat. Hist. PI.' (Eng. Ed. i, II, pp. 318-31). 



According to this investigator the significance of crowded inflorescences (Com- 

 positae, Umbelliferae, &c.), lies chiefly in the crossing that results between neigh- 



FlG, 2. Geiiono^amywith adhesive pollen {a.i\.er K^Tj\<tY). (i) Crossing; of branches of the styles of 

 adjacent florets in the capitulum of Eupatorium cannabinum. (2) Longitudinal section through the 

 upper parts of a young floret of Eupatorium : the two branches of the style lie parallel to one another, 

 enclosed in the anther-cylinder, which is again surrounded by the corolla-tube, (3) Umbellule of Chaero- 

 phyllum aromaticum : the true hermaphrodite florets are open, the pseudo-hermaphrodite pollen-florets 

 still closed. (4) The same umbellule : the true hermaphrodite florets are now without stamens, the pseudo- 

 hermaphrodite florets are open, pollen is dropping from the anthers of the latter upon the stigmas of the 

 former. 



bouring flowers of the same plant. In numerous Compositae belonging to the 

 group Liguliflorae, the spreading branches of the stigmas of adjacent florets intertwine 

 at the end of the period of maturity, so that pollen entangled in the hairs of the 

 style-branches comes into contact with the papillated stigmatic surfaces of the neigh- 

 bouring florets. Geitonogamy is also favoured by the fact that the capitula close 



