160 



THE STRUCTURE OF FLOWERS. 



In addition to slow and seemingly spontaneous move- 

 ments, to which all organs of a flower are liable, there are 

 mary rapid actions, brought about by the direct means of 

 external stimuli applied to them. Thus Indigofera and 

 Genista are two genera in which the claws of the petals are in 

 a great state of tension when the flower is open, and the 

 moment they are touched it explodes. The claws, from 

 having been horizontal, curl down- 

 wards, and the staminal tube with 

 the included pistil is jerked up- 

 wards. Thus Fig. 47, a, represents 

 a flower of G. tinctoria just expanded. 

 On passing a pencil point down the 

 front of the standard, the wings and 

 keel petals drop vertically, as seen 

 in Fig. 47, 6, looked at from the 

 front. The staminal tube now lies 

 against the standard. The keel, 

 from its extreme tension, splits 

 where it curls at the base, and be- 

 comes wrinkled in fi'Ont, as seen in 

 Fig. 47, c. 



There is a plant of the order 

 Convolvulaceoe, the corolla of which 

 ^. ,^ ^ .. .. ^ . I, actually closes on receivino: a me- 



Fig. 4:1.— Genista tinctoria: a, he- "^ o 



fore, b, after explosion ; c, claws chanical toUch. M. H, Dutrochct, 

 of keel. 



after observing that the movements 

 of Mimosa pudica and Dioncea muscijpula are all in one 

 direction only, as also of the stamens of Cactus opuntia and 

 Berheris, adds : •' Mais il est quelques cas oil cette incurvation 

 oscillatoire s'effectue dans plusieurs sens dilferents, tel est, 

 par exemple, le phenomene que presente une plante du genre 

 Ypomcea, observee aux Antilles par M. Turpin, plante encore 



