THE MOVEMENTS OF PLANTS. 



39 



&c. Thus in Silene nutans the petals unfold and curl up, re- 

 opening again as night approaches. It thus renders the flower 

 visible to nocturnal visitors, as moths. In some leguminous 

 plants, as Genistas, the corollas " explode." This is due to the 

 claws of the petals being in a high state of tension when the 

 flower is just ready to expand. Others, as in the Medicagos, 

 the staminal tube is irritable, and causes the flowers to burst 

 open in an analogous but not identically the same way. In 

 Berberis and Helianthemum vulgarc, the rock Rose, the stamens 

 are highly irritable to a touch, approaching the pistil in the 

 former, but receding from it in the latter case. In the Musk and 

 allied plants the two flap-like stigmas move together if touched, 

 while in Stylidium the style swings violently from one side of 

 the flower to the other if it be irritated at the base. 



Complicated movements occur in the fruiting stages of Tri- 

 folium subterraneum, fully described by Darwin.* 



Movements during the Dehiscence of Fruits. — These 

 cases are mostly of a quite different class of phenomena, and are 

 not characteristic of living protoplasm; for the organs are 

 quite dead and the movements are due to loss or gain of water, 

 elasticity of tissues, &c, and are mechanical. This is well seen 

 in the twisting of the awns of the fruit of Erodiwn, in the 

 elastic and twisting valves of Balsams and of Cardamine 

 hirsuta, as well as in the bursting of anthers and sporanges of 

 Ferns. 



Conclusion. — All the movements referred to, excepting the 

 last, and many more might be described, illustrate but one of 

 the many properties possessed by living protoplasm, viz. its 

 sensitiveness or irritability, by which it can respond to external 

 forces ; and, while doing so, it proceeds to build up tissues which 

 permanently supply the plant with highly adaptive structures. 

 For all the phenomena of climbing, of the metamorphoses of 

 organs into climbing structures, have undoubtedly come into 

 existence in response to the direct action of the environment. 

 Since there is no evidence that any structure in plants has ever 

 been originally developed before its use existed, or in anticipation 

 of such use, but solely in consequence of it. 



* Movements of Plants. 



