1903 Nervous Mechanisms of Plants 323 



Mimosa pudica t the sensitive plant, growing wild in 

 hot countries and occasionally seen in greenhouses in this 

 country, has remarkably sensitive compound pinnate leaves, 

 which on being roughly handled or shaken bend downwards, 

 the pinnae also closing together. At the approach of night 

 the leaves are said to behave in the same manner. At the 

 base of the leaf-stalk, and at the bases of the petioles of 

 each leaflet, there is a mass of cells called a pulvinus, 

 composed of parenchyma, which directly the leaves are 

 agitated lose their turgidity and fall, unable to support the 

 weight of the leaf. Directly each cell becomes filled with 

 water again the petiole returns to its usual position. This 

 may be done to frighten away browsing animals, or to give 

 the plant an appearance of withering. 



The common yellow Mimu/us, the Monkey Flower, of 

 our gardens, usually handsomely speckled with rich claret 

 brown, as well as the wild M. luteus and the sweet-smell- 

 ing musk, exhibits a curious movement of the stigma. 

 The stigma in all the species is composed of two broad 

 divergent lobes, usually rolled back from one another. On 

 being touched these lobes close rapidly up and lie flat, one 

 on the other. No doubt we have all, at one time or 

 another, sat playing interestedly with a plant of Mimulus^ 

 tickling the lobes of the stigmas with a pencil or other 

 handy weapon, watching the closing stigmas, or waiting for 

 their gradual rolling back again open-mouthed as before. 

 This wonderful little trap-like action is to ensure the pollen, 

 brought by a wandering insect, adhering to the stigmatic 

 surface. We find that both the inner and outer surfaces of 

 the lobes are irritable, and that the movement goes on 

 repeatedly, even when the corolla has fallen away from 

 the calyx (as is so quickly the case), until pollen is received 

 upon the stigma, and it is active no more. 



Another instance of rapid movement is to be seen in 

 stamens of the Barberry, either Mahonia or Berberis will serve 

 for the experiment, the former is the better flower as it is the 

 larger. The stamens stand in a ring within the petals and 

 surrounding the pistil ; if the base of one stamen is touched 

 the whole stamen falls quickly forward towards the stigma, 

 or the body of the insect which has set up the excitement. 



