Fertilisation of Scrophularia aquatica and S. nodosa. 381 



geniculate bases of the filaments of tlie external stamens 

 {ft). In these sulci the nectar collects as two droplets {nf), 

 one on each side of this ridge; and in protected flowers 

 these droplets ultimately coalesce to form an adherent film, 

 which creeps along the roof of the corolla. By this means 

 the anthers are secured from being wetted, and the nectar 

 is rendered easily visible from the outside. 



A striking feature in the sexual evolution of the flowers 

 of Scrcphularia is the proterogynous dichogamy which they 

 exhibit, the stigma reaching maturity and moving into the 

 position for cross fertilisation before the stamens begin to 

 rise from the floor of the corolla. 



In the young unopened bud the terminal portion of the 

 style is bent back superiorly, and points towards the nectary, 

 but by a progressive unbending the stigma is brought to 

 the mouth of the corolla ; and when the flower opens the 

 style is still bent up, and the stigma occupies a position in 

 tlie centre of the aperture of entrance, but behind its plane 

 (fig. 1,^). It is in this situation, or at some point between 

 it and the horizontal position subsequently attained, that 

 cross-fertilisation normally occurs. If fertilisation is 

 efi'ected, the style descends and becomes curved in the 

 opposite direction, so as closely to clasp the lower lip (fig. 

 3) ; but if fertilisation is prevented, the style remains 

 projecting horizontally from the mouth of the corolla (fig. 

 2) until long after all the stamens are forward, for the 

 purpose, apparently, of ensuring self-fertilisation if cross- 

 fertilisation fails. 



Darwin, in speaking of the movements of the sexual 

 organs,* says: — " In Scrophularia aquatica the pistil is bent 

 downwards from the mouth of the corolla, but it thus 

 strikes the pollen-dusted breasts of the wasps which habi- 

 tually visit those ill-scented flowers." That this decurva- 

 tion of the style, how^ever, is a consequence of fertilisation, 

 as Muller pointed out, and not a movement made to aid it, 

 may be seen by watching protected flowers, or by this 

 simple experiment. On one raceme I selected two equally 

 developed young flowers with their styles bent up, and put 

 pollen on one and not on the other. In about four hours 

 the style of the one which was fertilised was completely 

 decurved, while in the other it remained horizontal. 



* Forms of Flowers, p. 147. 

 TRANS. EOT. SOC. VOL. XVI. 2 C 



