68 PHARMACEUTICAL BOTANY 



The most highly specialized form of thigmotropism observed in 

 plants appears to be found in Mimosa Spegazzini, a member of the 

 Bean family. According to Steckbeck "when a mechanical stimu- 

 lus, such as a forceps pinch, is applied to one of the terminal secon- 

 dary leaflets after a latent period of less than Y second, the leaflet 

 stimulated rises and its partner almost at the same time. The 

 stimulus is then carried down the midrib, the pairs of secondary 

 leaflets closing in order; in 9 seconds all the secondary leaf lets, have 

 closed, the midribs converge followed in 3 seconds by a drop of the 

 entire leaf. The stimulus moves up the other leaflet with the result 

 that the secondary leaflets close in order. * In 20 seconds after the 

 stimulus has been applied all of the secondary leaflets are closed. 

 The stimulus is propagated through the stem to other leaves." 1 

 (Figs. 31 and 32.) 



4. Reproduction. Protoplasm also shows a very remarkable 

 ability to increase and to give off detached portions which retain 

 the infinitely complex peculiarities and properties of the original. 

 The process, moreover, may be continued indefinitely. 



Other physiological characteristics might be added, but the above 

 are mentioned as the most satisfactory criteria by which living may 

 be distinguished from non-living matter. 



PROTOPLASMIC CELL CONTENTS 



Protoplasm consists of four well-differentiated portions: 



(a) Cytoplasm, or the foamy, often granular matrix of protoplasm 

 outside of the nucleus. 



(b) Nucleus or Nucleoplasm, a denser region of protoplasm con- 

 taining chromatin, a substance staining heavily with certain basic 

 dyes. 



(c) Nucleolus, a small body of dense protoplasm within the 

 nucleus. 



(d) Plastids, composed of plastid plasm, small discoid, spheroidal, 

 ellipsoidal or ribbon-shaped bodies scattered about in the cytoplasm. 



1 "The comparative histology and irritability of sensitive plants" by D. W. 

 Steckbeck in Contributions from The Botanical Laboratory of the U. of Pa., 

 vol. IV, No. 2, p. 217, 1919. 



