VEGETABLE IRRITABILITY. 321 



that the movement seemed to be owing. The leaflets remain flat and 

 do not fold on themselves. It is said that by arresting the vital 

 actions going on in the leaflets, by giving them a coating of gum, and 

 thus preventing transpiration and respiration, the movements are 

 stopped, and that they recommence when the gum is removed by 

 water. Cutting a leaflet across, and only leaving a small portion of its 

 lamina attached to the petiolule, does not immediately stop the move- 

 ment of gyration. In such a case, however, the motion ultimately 

 ceases, while it continues in the uncut leaflet. So also, if a leaflet is 

 divided longitudinally into two parts, each of them continues to move 

 for a time, but the motions cease as the process of desiccation goes on. 



664. There are occasionally cellular prolongations from the leaf, 

 which, when touched, cause folding. Thus, in Dionaea muscipula, 

 or Venus's fly-trap, the lamina is articulated to the petiole, and consists 

 of two free portions which are united together, by a joint along the 

 midrib. On the upper side of each part of the lamina are situated 

 three hairs with swellings at the base, and when these hairs are 

 touched, the halves approach each other from below upwards, so as 

 to enclose any object, as a fly, which may happen to light on them. 

 Similar movements, but in a much less obvious manner, are said to 

 take place in the leaves of Droseras or Sun-dews. The movements 

 are attributed to the same causes as those already mentioned, but 

 the ultimate object is not known. 



665. Movements take place in some parts of the flower, occasionally 

 with the view of scattering the pollen on the stigma. The stamens 

 of various species of Berberis and Mahonia, are articulated to the torus 

 or thalamus, and when touched at their inner and lower part, move 

 towards the pistil. In Parnassia palustris, the stamens move towards 

 the pistil in succession to discharge their contents. The Helianthe- 

 mum vulgare or common Kock-rose, exhibits staminal movements 

 also connected with the bursting of the anthers. Morren has noticed 

 sensitiveness in the androacium of Sparmannia africana and Cereus 

 grandiflorus. In the Nettle and Pellltory, the filaments are confined 

 in a peculiar way by the perianth, and at a certain period of growth 

 they are released so as to allow their elasticity to come into play, by 

 means of which the pollen is forcibly scattered (^[ 497). In Goldfussia 

 or Ruellia anisophylla, the style has a curved stigmatic apex, which 

 gradually becomes straightened, so as to come into contact with the 

 hairs of the corolla, upon which the pollen has been scattered ; and in 

 Mimulus and Bignonia (fig. 406), the stigma has two expanded lobes 

 which close when touched, a movement apparently in some way con- 

 nected with fertilization. In the Passion-flower, and some Cacti, the 

 styles move towards the stamens. The species of Stylidium have the 

 filaments and styles united in a common column, at the upper part of 

 which the anther-lobes and stigma are placed. The column often 



