2 5 6 



BOTANICAL GAZETTE 



[SEPTEMBER 



of the roots observed. In another series of experiments, seedlings 

 grown at 20 C. were put directly into the heated thermostat. 



Curvatures. — When seedlings of Raphanus sativus have been in 

 the thermostat 2 hours, the roots show the following reactions: 



Positive 



7-15 



-°c. 



No curvature 



°c. 



16-23 



Positive 



24-36 c 



Negative 



°c. 



38-51 



At the higher temperatures the curvature occurs very quickly. 

 Roots grown at 20 C., when put into the thermostat at 45 C, give 

 a positive curvature in 5 minutes. This quickly goes over into a 

 negative curvature, so that within 20 minutes there is a strong 

 negative curvature. The explanation of this double curvature, of 

 course, is that as the temperature of the root rises to 3 8° C. there 

 is a positive curvature; when the root temperature has reached 

 45° C, a negative curvature begins. It should be remembered that 

 the side of the root toward the hot end of the thermostat is always 

 at a slightly higher temperature than the opposite side- At the 

 lower temperatures the roots react less rapidly, requiring i-5~ 2 

 hours for complete reaction at 7-1 5 C. 



TABLE I 



Thermotropic curvatures of roots 



Positive 



I. 



2. 



Raphanus sativus 

 Pisum sativum . . 



3. 



5. 



6. 



— (Wortmann) .... 



Sinapis alba (Klercker) 

 Helianthus annuus 

 (Klercker) 



Phaseolus multiflorus 

 primary roots (Wort- 

 mann) 



, secondary roots 



7" 

 8- 



8.5 

 14 



i5° C. 

 15° C. 

 3i° C. 

 29 C. 



No curvature 



16-23 C. 



I 7-29 C. 



Positive 



24-36° C. 



/ 



(Wortmann) 



None 



None 

 io-?°C.* 



8-22 C. 



Negative 



38-5 1° c. 



74-50 C 



34-50 c. 

 None 



15-40° C. 



22 



-5°° Q. 



?- 4 o° C* 



* Wortman-!* obtained positive curvatures at io° C. and negative curvatures at 40 C, but made no 

 investigations at the intermediate temperatures. 



roots 



Raph 



After one hour in the 



thermostat all the roots at temperatures from 34 to 50° C. showed 

 negative curvatures; and in 2.5 hours 80 per cent of those at 



