294 



BOTANY 



pass at regular intervals from one condition to the other. The 

 daily periods are the result of the stimulus imparted by the light, 

 the periodic action of which induces the regular changes of position. 



Fie. 236. Amiela zygoma-is, showing <liurn;il anil nocturnal i>osition of leavi--,. 



If, however, the external stimulus ceases to operate, the internal dis- 

 position still continues for some time to give rise to visible after-effects 

 (p. 261), until finally, from the abnormal conditions, an abnormal 



Fio. 23'. Mimosa pvdicv, with leaves in normal, diurnal fosition ; to the rij,'ht, in the position 

 assumed on stimulation ; B, inflorescences. 



state of rigor (light rigor, dark rigor) and symptoms of disease 

 are manifested ( 98 ). 



Only a few plants respond with pronounced variation movement* 

 to mechanical irritation (shock, friction, injury). These alone were 



