AUTOMATIC MOVEMENTS. 345 



like so many springs, until the anthers open, and the pollen absorbs 

 the glutinous matter that confines them, when they fly upwards 

 elastically, throwing the pollen in the direction of the stigma. The 

 bursting of the fruit of the Squirting Cucumber (Momordica Elate- 

 rium), and the elastic dehiscence of the Balsam, or Touch-me- 

 not (Tmpatiens), are also due to mechanical or endosmotic (37) 

 causes ; and therefore are not to be adduced as instances of vege- 

 table irritability. 



659. Automatic Movements, A few plants are known which exe- 

 cute brisk and repeated movements irrespective of extraneous 

 excitation, and which, indeed, are arrested by the touch. An in- 

 stance of such spontaneous and continued motion, of the most re- 

 markable kind, is furnished by the trifoliolate leaves of Desmodium 

 gyrans, an East Indian Leguminous plant. The terminal leaflet 

 does not move, except to change from the diurnal to the nocturnal 

 position, and the contrary ; but the lateral ones are continually ris- 

 ing and falling, both day and night, by a succession of little jerks, 

 like the second-hand of a time-keeper ; the one rising while the 

 other falls. Exposure to cold, or cold water poured upon the 

 plant, stops the motion, which is immediately renewed by warmth. 

 In several tropical Orchideous plants, and especially in a species of 

 Megaclinium, one of the petals executes similar and perfectly spon- 

 taneous automatic movements. 



660. Free Movements of the Spores of Algae, The spores of many 



of the lower Algae are now known to exhibit a peculiar active state 

 at the time of their discharge from the parent cell, when, for some 

 moments, or usually for several hours, they behave like infusory 

 animals, executing free, and to all appearance spontaneous, move- 

 ments in the water, until they are about to germinate. This singu- 

 lar movement was first detected, many years ago, in Vaucheria. In 

 Fig. 71, (p. 67,) we see the manner in which the spore is formed ; 

 and in Fig. 72, the mode in which it is discharged : also, on a 

 larger scale, in Fig. 467. It at once begins to move freely in the 

 water, and continues to do so for some hours, when it fixes itself 

 and begins to grow (Fig. 469). Its movements, moreover, may be 

 enfeebled or arrested by the application of a weak solution of opi- 

 um or of chloroform. Through these means it has been ascer- 

 tained that they are caused by the vibrations of minute cilia which 

 cover the surface, which are rendered visible by thus enfeebling 

 their rapid movement, and which exhibit the closest resemblance 



