308 Movements of Plants. 



been found that if the valves be placed in a fluid more dense 

 than that which the valves contain, such as syrup or gum- 

 water, the fluid will be drawn off from their ceils according to 

 the same law of Endosmose ; and the cells of the exterior will 

 be emptied soonest, on account of their being larger and fuller 

 than the others ; so that the valves become straight, and even 

 curl outwards. But if they be placed in water, the Endos- 

 mose, still taking place towards the side on which the fluid i a 

 most dense — viz. the interior cells — will distend them still 

 more, and cause the valves to curl inwards more powerfully 

 than at first. 



Another instance of movement which may be explained in a 

 similar manner, is that of the seed-vessel of the Squirting Cu- 

 cumber, (Momordica Elaterium.) This, when ripe, very rea- 

 dily separates from its stalk ; and its pulpy contents are vio- 

 lently forced out from the aperture thus left. The pulpy mat- 

 ter surrounding the seeds occupies the centre of the fruit, and 

 by its own increase in amount, distends the cavity ; when, 

 therefore, an aperture is formed in any way, the distention is 

 relieved by the violent contraction of the elastic walls. 



Such explanations, however, will by no means account for 

 all the evident movements of plants ; and it is necessary to 

 suppose their living tissues endowed with a property by which 

 they are enabled to contract upon the application of a stimu- 

 lus, just as do the muscular fibres of animals. The vegetable 

 kingdom affords many examples of this kind of contractility. 

 Thus, if the leaves of the common Wild Lettuce be touched 

 when the plant is in flower, the part will be covered with a 

 milky juice, which is forced out through the stomata by the con- 

 traction of the cells or vessels beneath. Again in the flower of 

 the Barberry, if the base of the stamen be touched with the 

 point of a pin, the filament will bend over so as to strike its an- 

 ther against the style. • This movement is undoubtedly con- 

 nected with the process of fetilization ; and it must be fre- 

 quently caused by the touch of insects. There is a curious 

 New Holland plant (Stylidium), sometimes cultivated in green- 

 houses, which has a tall column arising from the centre of its 

 flower, and consisting of the stamens and style united. This usu- 

 ally hangs down over one side of the flower, but if it be touched 



