668 PLANT RESPONSE 



Effect of temperature on autonomous torsion. — In 

 order to take a record of these torsional movements, a stem 

 is taken and held securely fixed at one end — say the lower — 

 the other being left free. On this free end, the mirror, 

 by the reflected light from which the record is to be made, 

 is attached ; and a long thread from above is tied to the tip 

 of the specimen, in order to prevent its falling to one side 

 by its own weight. The limpness of this supporting thread 

 allows the torsional movements of the specimen to occur 

 without hindrance. 



In taking records of the natural torsional response of 

 plants at various temperatures, I have obtained results which 

 are in a general way similar to the records made of longi- 

 tudinal growth-response (p. 446) — that is to say, the response 

 is enhanced up to the optimum, which is at or near 35 C. 

 Above this, response is diminished. These facts will be seen 

 from the following table, which gives the absolute rate of 

 the angular movements of the torsional response at different 

 temperatures. 



The specimens employed in these and the following 

 experiments were climbing stems of Parana pamculata, a 

 plant belonging to the Campanulacece, which normally ex- 

 hibits a strong negative torsion. 



Table giving the Absolute Rate of Angular Movements 

 01 Torsional Response at various Temperatures 



Temperature 



28 C. 

 32 C. 

 35° C. 

 37° C. 



Torsional movements 



•09 per minute 

 •18° 



•282 „ 

 •18 „ 



An interesting effect was observed, however, in this case 

 of torsional response, when the temperature was raised 

 above 43° C, which was apparently different from what 

 occurred in ordinary longitudinal growth-response at the 

 same temperature. It was found in the latter case that at 

 44° C. or thereabouts growth underwent an apparent arrest ; 



