420 



MOVEMENTS. 



1086. The leaflets of numerous plants exhibit a peculiar degree 

 of sensitiveness even to a slight touch. Among these are sev- 

 eral species of Mimosa and Oxalis. 

 The plant which has received the 

 fullest investigation is the easily 

 cultivated 



1087. Mimosa pudica (the Sen- 

 sitive plant). This has compound 

 leaves consisting of four long leaf- 

 lets, each of which is divided into 

 numerous minor leaflets arranged 

 in pairs. At the base of each leaf- 

 let, and also at the base of the 

 petiole, there is a pulvinus, com- 

 posed of peculiar cells. On the 

 upper half of the pulvinus these 

 are thicker-walled than on the 

 lower ; most of them contain round- 

 ish globules made up of a strong 

 solution of tannin in water, surrounded by a film of some albu- 

 minoid matter. These globules are not, 

 however, of any significance as concerns the 

 motility, since they are found in the paren- 

 chyma of the bark of some ligneous plants 

 (see 953). 



1088. When a fully spread leaf is touched 

 at its extremity the many leaflets succes- 

 sively close in pairs, the upper surfaces 

 approaching and the tips falling somewhat 

 forward; the four 

 branches of the leaf 

 then draw near each 

 other, and the main 

 petiole inclines 

 downwards and 

 finally droops pas- 

 sively at the joint. 

 The recovery from 

 this position of col- 

 lapse takes place in 

 a few minutes, generally in about a quarter of an hour. 



Fm. 190. Al.lrovanda vesiculosa; the lower illustration shows the expanded leaf 

 much enlarged. 



FIG. 191. Mimosa pudica. 



