THKRMONASTIC PHENOMENA 307 



(rise of temperature) are of opposite character, radiation 

 inducing contraction, and rise of temperature, expansion. 

 It is therefore advisable to distinguish the thermal, or 

 temperature etlect, from the radio-thermal effect of infra- 

 red radiation. 



TWO TYPES OF RESPONSE. 



As regards the eff'ect of variation of temperature I 

 shall proceed to show that there are two distinct types, 

 which I shall, for convenience, distinguish as the Positive 

 and Negative. 



Positive thermonastic raaction is exhibited by organs in 

 which the upper half is the more excitable. Response to 

 rise of temperature is by doivnward or outward move- 

 ment. In floral organs this finds expression by a move- 

 ment of opening. In illustration of this may be cited the 

 examples of the well known Crocus and also of Zep/ui- 

 raitthes. 



Negative thermonastic movement is shown by organs in 

 which the lower half is the mora excitable. Here the 

 response to rise of temperature is by an upward or inward 

 movement. I shall show that an example of this is 

 furnished by the flower of Nytnphcea which closes under 

 rise, and opens during fall of temperature. 



POSITIVK THKRMONASTIC RESPONSE. 



Ref2Jonse of Zephyranthes : Ej'periment 11 S. — Viewed 

 from the top, the inner side of the petal of a tlower is 

 the upper side. The Crocus flower under rise of temper- 

 ature opens outwards by expansion of the inner side, which 

 must be the more excitable. As Crocus was not available 

 in Calcutta, I found the flower of Zepkyranthes (some- 

 times called the Indian Crocus) reacting to variation of 



