GEITONOGAMY. 32T 



pollen by insects occurs but seldom in this plant, so that from the many ovaries in 

 the inflorescence of Uremu^'us usually only a few fruits are matured. This is the 

 more remarkable as these flowers have remarkably long-lived stigmas, a peculiarity 

 which is generally very advantageous in bringing about cross-pollination. The 

 stigma is already mature when the perianth opens; when the tips of the perianth 

 roll back and assume the form of aphides (see p. 171), and when the style moves 

 like the hand of a watch towards the axis of the inflorescence, the stigma is still 

 receptive, and remains so even when the style has again straightened and assumed 

 an oblique upward direction. 



A peculiar instance of geitonogamy is observed in Allium Victorialis. Each umbel 

 is composed of flowers of very different ages. Before the first flowers bend over, 

 wither, and shrivel up, their pollen- covered anthers project well over the edge of the 

 perianth. In the younger flowers, at the same time, the anthers are still closed and 

 covered by the perianth-leaves, but the stigmas are ripe and project beyond them. 

 These young and hitherto short-stalked flowers are now raised by the elongation of 

 their pedicels and inserted between the older flowers, so that, as a matter of course, 

 their stigmas are brushed by the pollen of the older flowers, if it does not indeed fall 

 on them. 



The geitonogamy in the Bistort (Polygonum Bistorta) is very strange. It is 

 rendered rather complex, as a peculiar distribution of the sexes is combined with a 

 pronounced dichogamy and a peculiar way of opening. The inflorescence, which 

 looks like a spike, is really composed of numbers of tiny two -flowered groups 

 crowded together. One of the two flowers of each little group is long-styled and 

 truly hermaphrodite, while the other contains a short style, well-formed stamens, 

 and a rudimentary ovary which develops no further. It is therefore a pseudo- 

 hermaphrodite staminate flower. In each group the long-styled hermaphrodite 

 flower opens first, beginning at the base of the apparent spike and gradually 

 working up to the top. The staminate flowers do not get their turn until the 

 highest of the long-styled flowers has opened; but after this they behave exactly 

 like their neighbours, i.e. the lowest develops first. The long-styled flowers are pro- 

 tandrous. At the commencement of flowering the pollen-covered anthers project 

 a millimetre from the perianth; the styles, however, are still short and hidden in the 

 interior. At this time pollen can only be removed from the flowers. Then the 

 anthers fall oflf and the styles elongate so as to protrude some 3 mm. beyond the 

 perianth. The whole spike is at this stage beset with receptive stigmas which can 

 only be fertilized by insects with pollen from other plants. But this state of things 

 does not last long, for now the staminate flowers open one after another in quick 

 succession. Their anthers, containing abundance of pollen, protrude 3 mm. beyond 

 the perianth and come into contact with the still receptive stigmas of their neigh- 

 bours, so that geitonogamy results. As soon as this is efiected the staminate flowers 

 become detached from the axis of the spike and fall to the ground. This geitono- 

 gamy is of course useless to the stigmas which have already received pollen from 

 other plants by insect agency, but it is of the greatest importance to the flowers 



