144 HENRY D. HOOKER, JR. 



At higher temperatures, in these cases from 38° to 46°C., the 

 roots reacted with negative thermotropism, at lower tempera- 

 tures, from 12° to 15°C., with positive thermotropism. The nega- 

 tive bending occurred regularly and with precision; the positive 

 was much more variable, and did not result in every case. No 

 attempt was made to determine the critical temperature. The 

 following experiments illustrate. 



Experiments With Ervum Lens. First Series 



First Experiment. Seeds of Ervum Lens were sprouted in moist sawdust. After 

 forty-eight hours, those were selected with radicles 2 cm. long. Eight seedlings 

 were aligned with T" and eight more with T'". Forty-five minutes after the light- 

 ing of the gas, T' registered 43°C. and T'" 13°C. In three-quarters of an hour 

 more, six of the roots by T' had bent negatively. After three hours and a half 

 more, the other two by T' had bent, and three of those at T'" were bent posi- 

 tively. All the bent roots pointed away from the wall toward the middle. 



Second Experiment. In the second experiment also with Ervum Lens, the radi- 

 cles were but 1 cm. long. Six seedlings were aligned with T" and 7" " respectively. 

 Three-quarters of an hour after lighting T" registered 41° and T'" 12°C. 

 After three-quarters of an hour more, five roots by T" were negatively bent. At 

 the end of four hours more, two roots by T'" were positively bent; of those at 

 T' all of which were now bent, four were especially strongly curved. At the end 

 of the experiment T' was at44°C. and T'" at 14°C. 



In these experiments the sawdust was observed to become very 

 dry along the heated side because of the rapid evaporation. For 

 this reason, in all subsequent experiments a cover was used, a 

 device suggested by Klercker's apparatus. This simple change 

 noticeably increased the time required for the reaction, as will be 

 observed in the following experiments. 



Second Series. 



First Experiment. Ervum Lens seedlings were used with radicles approximately 

 2 cm. long. Eight were placed on either side. Forty minutes after lighting T" was 

 at 45° and T'" at 12°C. After two hours and twenty minutes, three roots at T' 

 were negatively bent. After six hours more, two roots by T'" were bent positively 

 No change occurred in those left at T". At the end of the experiment T' was at 46° 

 C. and T'" at 15°C. 



Second Experiment. In the next experiment the radicles were but 1.5 cm. long, 

 otherwise as in the last one. Three-quarters of an hour after lighting T' was at 

 38" and T'" at 11°C. After three hours five roots by T' were negatively bent. 



