PROTOPLASMIC MOVEMENT. 387 



velocity of the movement increases, as a rule, witli the tem- 

 perature, and, indeed, in all special cases a definite constant 

 velocity corresponds to a definite degree of temperature. This, 

 however, is no longer the case if shortly before, a rapid and ex- 

 tensive fluctuation of temperature has taken place. Such 

 fluctuation acts like a mechanical or electrical excitation, and 

 will be spoken of later. For similar increments of temperature, 

 the increase of velocity appears in many cases to be greater, the 

 higher the absolute temperature. 



Naegeli,^ in the terminal cell of Nitella syncarpa, 

 which was slowly warmed under the microscope, observed that 

 a distance of O'l mm. was traversed by the rotating layer in 

 60 sec. at 1° C, in 24 sec. at 5° C, in 8 sec. at 10° C, in 3-6 sec. 

 at 20° C, in I'S sec. at 31° C, in 0-6 sec. at 37° C. Schultze 2 

 has shown, on the contrary, that the granular streaming in 

 Miliola, which at ordinary temperatures is already very rapid — 

 0'2 mm. in a second — cannot be accelerated by further warming. 



There is apparently in every case a certain higher limit of 

 temperature at which the movement attains its highest velocity. 

 This optimum temperature generally lies several degrees below 

 the maximum temperature compatible with movement. If the 

 temperature rises above the optimum the movement indeed be- 

 comes just at first even more active, but dies out after some time. 

 There is generally some delay before this occurs, but this is the 

 less the nearer the prevailing temperature to the maximum. If 

 the temperature attains the maximum, all movement stops in a 

 moment. The protoplasm then enters upon a condition of ap- 

 parent death or rigor — temporary heat rigor, heat tetanus — in 

 which it remains, as though under continued artificial stimula- 

 tion. It is drawn together so as to expose the smallest sur- 

 face, and is only relaxed when cooling occurs, when, and in 

 which case only, the movements are able to start once more. 

 The optical properties of the protoplasm are not necessarily 

 altered in this condition. 



' C, Naegeli, ' Beitriige zur wissensch. Botanik,' 2 Heft, p. 77, Leipzig, 

 1860. 

 * Max Schultze, * Das Protoplasma, &c.,' p. 47. 



