SENSORY ELEMENTS 



IS 



resultant reaction with that obtained from a normal and upright 

 specimen. 



21. Recovery of Normal Position after Shock. Jar a suit- 

 ably expanded specimen of Mimosa in such a manner that all of 

 its leaves drop and its pin- 

 nules close. Measure the 

 distance between the tips 

 of the closed pinnules and 

 mark position of tips of 

 leaflets. Note exact length 

 of time before the resump- 

 tion of the original position 

 begins. During this pe- 

 riod the contractile cells 

 are slowly regaining their 

 former degree of turgidity 

 by the reabsorption of the 

 previously excreted water. 

 Compare this period with 

 that of the amoeba or 

 streaming cells after shock. 



22. Sensory Elements. 

 Practically all of the epi- 

 dermal cells of the shoot 

 of Mimosa, except some 

 parts of the inflorescence 

 and the upper side of the 

 pulvinus are capable of receiving the mechanical stimulus and 

 converting it into an impulse which may be transmitted to distant 

 parts of the body. Even the cotyledons are slightly "sensitive." 



. When the pinnule is struck the effect is generally given direct to 

 the small pulvinus at its base, but the cells of the lamina are 

 capable of receiving the stimulus and transmitting its effects, as 

 may be shown if the pinnule is gently pinched, or snipped, or 

 touched with a small heated wire. 



Fig. 4. Section of pulvinus of Mimosa, a, 

 b t turgid parenchyma of upper and lower sides, 

 c, bud. d, parenchyma of stem. <?, pith. After 

 Green. 



