CHANGE OF POSITION OF ANTHERS AND STKi.MAS. 



short-styled flower. I shall return to the subject of heterostyly in the next chapter, 

 and will merely say here that there are also plants whose anthers and stigmas 

 present three kinds of arrangement. For example, in the Purple Loosestrife 

 (Ly 'thrum Salicaria) the flowers on one plant will have long styles, on anotln-r 

 medium styles, and short styles on a third plant; the two whorls of stamens in 

 plants with long-styled flowers are below the stigma; in the medium-styled flowers, 

 one whorl of anthers is above, and the other below the stigma; whilst in the short- 

 styled flowers both whorls of anthers are above the stigma We should also briefly 

 state here that the Eschscholtzia, which usually possesses four styles (figs. 288 5 and 

 588 e ), develops styles of unequal length in its flowers; in some flowers, which are 

 distinguished by their larger circumference, there are two longer and two shorter. 

 The longer styles receive the pollen from other flowers, and are adapted to cross- 

 fertilization, while the shorter styles are pollinated by the anthers standing close 

 beside them (fig. 288 6 ). There are also smaller flowers containing four styles which 

 .are all so short that they do not project above the pollen -producing anthers 

 (fig. 288 5 ). We can only briefly touch upon the remarkable Ranunculaceae and 

 Rosacese (Anemone baldensis, Pulsatilla alpina, vernalis, Ranunculus alpestris, 

 glacialis, Geum montanum, reptans, &c.) which develop pseudo-hermaphrodite male 

 flowers, as well as two kinds of hermaphrodite flowers, those with large ovary 

 .and few short stamens, and those with small ovary and numerous long stamens; 

 but it may be stated that the former are adapted to crossing, and the latter to 

 .autogamy. 



Another contrivance for promoting cross-fertilization is the interchange of posi- 

 tion of anthers and stigmas. Although this has been repeatedly mentioned already 

 (see pp. 250 and 276), it must again be described, since it represents one of the most 

 important contrivances for the crossing of hermaphrodite flowers, and can only be 

 -completely understood when regarded from this point of view. The change of 

 position consists essentially in this; the place occupied for some time by the ripe 

 stigma is assumed later by the pollen-laden anthers, and vice versd. Since this 

 position is directly in the path traversed by the honey-sucking insect as it enters, 

 the pollen is brushed on to the stigmas in one flower and collected from the anthers 

 in another a condition necessarily leading to cross-fertilization. This change of 

 position is brought about by spontaneous movements in the anther-filaments, or by 

 similar changes of direction in the styles. It may even happen that both the 

 stamen-filaments and the styles of the same flower alter their position and actually 

 exchange places. We may distinguish no less than ten different varieties of this 



change of position. 



In one group of plants, of which the Dwarf Leek (Allium Chvmatmoly) may 

 be taken as an example, the ripe stigma is seen in the middle of the newly-opened 

 flower, while the anthers are pressed back against the perianth-leave* 

 the anthers open and expose their pollen, they pass towards the centre by reason 

 -of the peculiar movement of their filaments till they come close to the , 

 .-and form a yellow ball. This is necessarily touched by an insect aa it enters the 



