414 SOURCES AND TRANSFORMATIONS OF PLANT-ENERGY 



The high energy of expansion and contraction in the stamens of 

 Cynareae and in the leaves of Mimosa enables these organs to raise a con- 

 siderable weight in addition to their own. According to Schilling 1 , a 

 stimulated leaf of Mimosa pudica returns to its original position after the 

 statical moment exercised upon the primary pulvinus has been increased 

 from two to four times by the attachment of weights. This is probably 

 due to the fact that the change of position produced by stimulation awakens 

 reactions directed towards the restoration of the original position ; and hence 

 a leaf slowly rises up again after it has been merely bent somewhat down- 

 wards by the addition of a weight without being stimulated. The exact 

 causal relationship of these phenomena is, however, not satisfactorily deter- 

 mined by Schilling's experiments, which also leave it uncertain to what 

 degree a similar power of reaction is possessed by other pulvini. In any 

 case, however, the mechanical factors concerned in the movements of 

 irritable pulvini and of the stamens of Cynareae have been more fully 

 explained than those involved in muscular movement. 



1 A. J. Schilling, Der Einfiuss von Bewegungshemmungen auf die Arbeitsleistungen d. Blatt- 

 gclenke von Mimosa pudica, 1895, p. n. 



