XLVIIL— DIURNAL MOVEMENT DUE TO VARIATION 

 OF TEMPERATURE AFFECTING GROWTH 



By 



Sir .7, C. Bose, 



Assisted by 



Lalit Mohan Mukerjee. 



It has been stated that ihere are two classes of diurnal 

 movements caused by variation of temperature ; one of 

 these is due to differential growth induced on two sides 

 of the organ, and the other is brought about by the 

 induced variation of geotropic curvature. The former may 

 be distinguished as Thermonastic, and the latter as 

 Thermo-gi'otropic movement. Before laying down the criteria 

 to distinguish the one class of phenomenon from the other, 

 it would be advisable to refer to the somewhat arbitrary 

 distinction that has been made between nastic and tropic 

 reactions. 



TROPIC AND NASTIC MOVEMENTS. 



The explanation, which I shall offer about the night 

 and day movements m plants, has been reached through 

 the study not only of pulvinated, but also of growing and 

 fully grown organs. A distinction is made between the 

 movement due to growth, and the 'variation movement' 

 due to change of turgor. I have shown (p. 239) that the 

 same diminution of turgor which induces a contraction in 

 a pulvinus, also induces in a growing organ an incipient 

 contraction, and retardation of growth. Enhancement of 

 turgor, on the other hand, induces in both the opposite 

 effect of expansion. Unilateral stimulus induces curvature, 



