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THE POPULAR SCIENCE MONTHLY. 



and a suitable temperature are necessary conditions. Repeated 

 stimulation at short intervals fatigues the organ, making it less 

 and less responsive, until finally all signs of sensitiveness disap- 

 pear, to return only after a period of rest. Certain chemical sub- 

 stances which are known to abolish or suspend the contractility 

 of animal protoplasm have been found to affect in a correspond- 

 ing manner the movements of barberry stamens. Thus nicotine, 

 alcohol, and the mineral acids destroy all power of movement. A 

 one-per-cent solution of morphine is similarly active, while curare, 

 the powerful nerve poison which leaves the contractility of 

 muscle unaffected, is found to exert no influence upon the stamens 

 of Berberis. The effect of arsenic and corrosive sublimate is to 

 render the filaments rigid and brittle, while if poisoned with 

 prussic acid or belladonna they become relaxed and flaccid. By 

 exposure for a short time to the vapor of chloroform or ether the 



FIG. 13. Series of anthers connecting the primitive form with that having valvular dehis- 

 cence: A, Podophyllum emodi ; B, PodopTiyllum peltatum ; C, hypothetical transition 

 form ; D, the barberry form. All somewhat diagrammatic. 



power of movement is suspended, but may return after removal 

 from the influence of the anaesthetic. 



Moreover, experiment shows that the part of the filament which 

 contracts is not necessarily the part touched that is to say, there 

 is a transmission of stimulus from cell to cell. So long as it 

 was believed that the contents of neighboring plant cells were 

 always completely separated by an imperforate wall, no satis- 

 factory explanation could be given of such a transference of im- 

 pulse, but now that modern microscopy has revealed the presence 

 of protoplasmic threads passing through the cellulose walls of 

 sensitive tissue, making the living matter continuous, the phe- 

 nomenon in question may be understood as a manifestation of 

 that fundamental property of protoplasm, irritability, to which 

 we also refer the sensitiveness of animals, even though it be ex- 

 hibited in a highly differentiated nervous system. 



Since the irritability of the stamens is found so commonly 



