DAILY MOVEMENT DUE TO THERMO-GEOTROPISM 565 



hundredth part of a degree above the predetermined tem- 

 perature. The automatic make and break of the current 

 takes place in rapid succession, and the temperature of 

 the chamber is thus maintained constant within tenth of 

 a degree, throughout day and night. 



Diurnal I'ecord uf Tropaeolum under constant tempera, 

 ture : Experiment 212. — The normal record of geotropically 

 curved Tropceolum is already given in figure 202. In repeat. 

 ing the recocd I maintained the plant at constant tempera" 

 ture for 24 hours ; the result of this is seen in the 

 first part of the record (Fig. 203). The thermal record 



Fifi. 203. — Abolition of diurnal itiovement in Trupwolnm under constant 

 temperature, and ita restoration under normal daily liuctuation. The upper 

 record is of temperature and the lower of plant movement. 



is practically horizontal, and the diurnal record of the plant 

 shows no periodic movement. The thermal regulator was on 

 the next day put out of operation, thus restoring the normal 



