72 PHYSIOLOGY OF STREAMING MOVEMENTS 



being too short, or too weak in character, for Lopriore has shown that 

 the Rontgen rays at first accelerate streaming in Vallisneria^ but that 

 if the action is prolonged streaming is retarded and the cells injuriously 

 affected. The influence of the absence of light or of temporary weak 

 illumination is so slight as to be negligible, and hence these results 

 are due to the direct action of the Rontgen rays, and prolonged exposure 

 to them seems to produce a distinct effect upon animal organisms also. 



With regard to the influence of the prolonged absence of light, 

 Dutrochet T found that streaming ceased in Char a after twenty-four to 

 twenty-eight days' darkness, but this was merely the result of starvation, 

 for the author has shown that if the darkeaed parts remain attached 

 to the parent plant, the cells may remain living and showing streaming 

 for five to eight weeks 2 . Light as such does not therefore form a directly 

 essential factor in the maintenance of streaming movements. 



SECTION 30. Mechanical Stimuli. 



That a retardation or temporary cessation of streaming may be caused 

 in Char a and Nitella by mechanical shocks has long been known 3 , although 

 Pfeffer has shown that mechanical vibrations exercise no effect upon 

 streaming in hair-cells of Hyoscyamus and Datura, while Hermann found 

 that mere contact or gentle rubbing with a soft brush produced no effect 

 on streaming in Nitella syncarpa 4 . Similarly regular (siren, organ-pipe, 

 violin) or irregular (explosions) vibrations of the air produce no perceptible 

 effect upon streaming in cells of Chara and Nitella upon which they freely 

 impinge. The inertia of the cell-wall and its fluid contents is, however, 

 very great as compared with that of the air, and hence it is still possible 

 that very violent vibrations of considerable amplitude might produce some 

 perceptible effect. 



Hermann states that rapid changes of pressure in the surrounding 

 medium (water) exercise no influence upon streaming in Nitella syncarpa. 

 His experiments were carried out by placing the cells in water in a flat 

 glass tube connected with a manometer tube filled with mercury. By 

 raising or lowering this tube, pressures up to twp atmospheres could be 

 obtained. If, however, a piston filled with water is used in place of the 

 manometer tube, a smart blow on the head pf the piston-rod will almost 

 always cause a temporary cessation of streaming, provided that the ends 

 of the two tubes are .closely approximated and connected by tightly bound 



1 i.e., p. 29. 



a Ewart, Journ. Linn. Soc., 1896, Vol. XXXI, pp. 563-4. 



3 Cf. Engelmann, Die Protoplasmabewegung ; Hermann, Physiologic, Ed. i, Heft I ;"Strasburger, 

 Jenaische Zeitschr., xil. 



* Pfeffer, Pflanzenphysiologie, ed. i, Bd. II, p. 390; Hermann, Protoplasmastromung, 1898, 

 p. 40. 



