226 



MOVEMENTS 



that some flowers {e.g. Lychnis vespertina) are closed by day 

 but open by night. 



Fig. 253. — Capitulum of 

 Dandelion open. 



Fig. 254. — Ditto closed. 



IRRITABILITY OF MOVING ORGANS. 



These regularly recurring (periodic) movements of leaves 

 and flowers are liable to be disturbed by changes in the 

 temperature or moisture of the air, or by changes' iii' the 

 illumination of the plant, These changes act as stiiiiuli and 

 cause "itiduced movements." If at daytime we put a Clover 



