404 PHOF. TH. W. ENGELMANN. 



warming, from 18° to 27° ; from 27° to 34°, and from 34° to 

 40°, the rotation stopped for a time, varying from some minutes 

 to an hour. 



Hofmeister^ observed a temporary cessation of the rota- 

 tion in a preparation of Nitella which was taken from 

 a room at a temperature of 18*5° C. into one at 5° C. and 

 left there for two minutes. The same thing ~ happened after 

 six to eight minutes with hairs of Ecbalium agreste, which 

 exhibiting active streaming at 16 — 17° C, were taken into a 

 temperature of 40° C, the protoplasmic network becoming 

 much simpler and quite motionless. The streaming commenced 

 again at the latter temperature only after a pause of from 

 half an hour to two hours, and, once started, attained in a few 

 minutes the activity normal to such a temperature. Rapid 

 cooling from 40° to 17° C. rendered the protoplasm of the 

 same object motionless. Again, " at numerous spots it had 

 formed knotty varicosities." The movements recommenced 

 only after seven minutes, and became once more normal 

 (temperature constant at 16° C.) only after eighteen minutes.^ 

 On rapidly warming the stinging hairs of Urtica up to 

 40° C. and higher, Schultze ^ often observed the same curious 

 changes of form of the protoplasm which Briicke has de- 

 scribed as occurring after strong shocks with the magneto- 

 electro-motor. (See above.) Kiihne^s and Hofmeister's ob- 

 servations upon the effect of rapidly freezing Tradescantia 

 cells have already been described. 



3. Light Stimuli. 



The greater number of kiuds of contractile protoplasm 

 appear insensible to light or changes of light. This is the 

 case, for instance, in the protoplasm of the colourless blood- 



' W. Hofmeister, ' Die Lehre von der Pflanzeuzelle,' p. 53; cp. also Hugo 

 de Vries, in 'Flora,' 1873, p. 25 (Hydrocharis morsus rante). 

 - Ibid., p. 55. 

 3 Ibid., p. 54. 

 * M. Schultze, ' Das Protoplasma, &c.,* p. 48. 



