250 TAKING UP OF POLLEN BY INSECTS. 



" revolver-flowers " the anthers are so placed with their pollen-covered faces in front 

 of the mouths of the tubes, that insects inserting their probosces are bound to rub 

 against them. 



The flowers of the Wild Mustard (Sinapis arvensis), Dvplotaxis, and several 

 other Cruciferous plants have anthers, which, after dehiscence, execute spiral twist- 

 ings with the object of turning the face covered with pollen away from the stigma, 

 and placing it near the spot where insects insert their probosces for the honey. 

 In other Cruciferse, with flowers somewhat resembling " revolver-flowers " in struc- 

 ture, although the approach to the honey is not straight through a tube, the stamens 

 exhibit characteristic bendings of the filaments with a view to bringing the anthers 

 into the line of entrance to the nectar. Thus, for instance, in the flowers of Kernera 

 saxatilis (see figs. 267 ^'^^ ^''), honey is only to be found on the two narrow sides of 

 the compressed ovary, although there are petals all round the ovary. Supposing 

 all the filiform filaments, whether in front of the narrow or of the broad sides of 

 the ovary grew straight up, only the anthers borne on the former would deposit 

 their pollen on the honey-sucking insects. In order to render the anthers situated 

 opposite either of the broad sides of the ovary which are destitute of honey liable 

 to be stroked by intruding insects, their filaments are bent at right angles, as is 

 shown in figs. 267 ^ and 267 ^''. By this means aU the dehiscent anthers of the 

 flower are brought into such a position as to be necessarily rubbed by insects when 

 they come to suck the honey. Movements of stamens, directed to the same end, 

 are also observed in numerous Caryophyllacese, Ranunculacese, Saxifragese, Cras- 

 sulacese, and Droseracese. The floral structure in the Caryophyllaeeous plants 

 coming under this category is similar to that of "revolver-flowers"; the petals are 

 unguiculate, that is to say, they are composed of an inferior very narrow part 

 inserted in the tubular calyx, called the claw or unguis, and a flat expanded region 

 above the calyx called the lamina. A groove runs down the middle of the claw 

 to the floral receptacle, and at the upper end of the groove, where butterflies are 

 to introduce their probosces, the lamina is sprinkled with bright-coloured patches 

 or speckles, and is furnished sometimes with scales arranged in pairs, or something 

 else of the kind to make the entrance conspicuous, and regulate and facilitate the 

 introduction of the proboscis. In these Caryophyllacese the anthers, just after 

 dehiscence, are so placed in relation to the entrance that butterflies must necessarily 

 smear their heads and probosces with pollen as they thrust the latter organ along 

 the grooves. After that has happened, the filaments bend to one side or stoop 

 down beneath the laminae of the petals, and then other stamens come into play, 

 their anthers being held, as the first were, in front of the grooves running down 

 the petals. In the Ranunculacese — Eranthis, Helleborus, Isopyrum, Nigella, 

 TroUius (see fig. 267 ") — a large number of stamens surround the central multiple 

 pistil in several whorls. They are themselves encompassed by a circle of very small 

 trumpet-shaped or tubular petals filled with honey, the so-called nectaries, and these 

 are in their turn surrounded by large floral leaves, white, yellow, red, or blue m 

 colour, which descriptive Botanists have designated as petaloid sepals. Shortly 



