262 ANGIOSPERMAE—DICOTYLEDONES 



fruticosa, which, according to Hermann Miiller (' Weit. Beob.,' pp. 244-5), 'S also 

 distinguished by its protogyny from the other Papilionaceae, these being typically 

 homogamous or protandrous (Taubert, op. cit.). 



Kuhn states (Bot. Ztg., Leipzig, xxv, 1867) that some genera include species 

 with cleistogamous flowers, e. g. Arachis L. , Chapmannia Torr. el Gray, Hetero- 

 carpaea Phil., Lesperdeza Rich., and Stylosanthes Swarlz. 



The following Papilionaceae have so far been recognized as self-sterile : — 

 Trifolium pratense, T. repens, T. incarnatum ; Phaseolus multifiorus, Lathyrus 

 grandiflorus, Vicia Faba, Erythrina sp., Sarothamnus scoparius, Melilotus officinalis, 

 Lotus corniculatus, Cytisus Laburnum (Darwin), Astragalus alpinus (Axell), Wistaria 

 sinensis (Gentry). 



193. Sarothamnus Wimm. 



Yellow, homogamous, hymenopterid flowers devoid of nectar; with explosive 

 mechanism and spirally coiled style. Only one effective visit possible. 



639. S. scoparius Koch (=Spartium scoparium Z.). (Darwin, Proc, Linn. 

 Soc, London, 1867, p. 358 ; Herm. Miiller, 'Fertilisation,' pp. 195-8, 'Weit. Beob.,' 

 II, p. 257; MacLeod, Bot. Jaarb. Dodonaea, Ghent, vi, 1894, pp. 329-32; Knuth, 

 'Bl. u. Insekt. a. d. nordfr. Ins.,' pp. 55-6, 152, ' Bloemenbiol. Bijdragen.') — The 

 flower mechanism of this species can only be liberated by humble-bees and the 

 honey-bee ; while smaller and less skilful Apidae, as well as a few Syrphidae and 

 beetles, are merely found collecting or devouring the pollen of already exploded 

 blossoms. The mechanism is described by Hermann MuUer somewhat as follows. — 



Insects are attracted by the large yellow flowers, and although these are 

 nectarless the vexillum is marked with streaks which converge below so that the 

 presence of nectar is suggested to insects. When a honey-bee settles upon a flower 

 that has not yet been visited, it grasps the alae with its middle and hind-legs, 

 and pushes its fore-legs and head under the middle of the vexillum. The alae 

 are therefore pressed forcibly down, and also the carina, of which the proximal 

 third is united with them by interlocking folds. The free upper edges of the 

 carina consequently begin to separate from base to tip, and as soon as they have 

 half done so, the five shorter stamens, which even in the bud dehisce upwards, 

 spring up and scatter some of their pollen on the ventral surface of the bee, without 

 disturbing it in its work. The cleft now rapidly extends towards the tip of the 

 carina till it reaches the point where the tip of the style presses against the united 

 part of the carinal petals, when a second and much more violent explosion takes 

 place. Until then the long style lies like a stretched spring in the carinal cavity, 

 the extremity of which it fills, while its end is pressed against the tip of the carina. 

 Scarcely, therefore, have the edges of the carina separated as far as this point, 

 when the style shoots out, and strikes the back of the bee with its papillose tip. 

 Immediately afterwards, most of the pollen swept out by the lamelliform part of 

 the style is thrown upon the back of the insect, while at the same time the five 

 long stamens, which have long since dehisced, bend inwards and spring out of 

 the carina. The visitor now frees itself from the style, which has usually coiled 

 round it, and collects the pollen still adhering to the anthers. This is so abundantly 



