THE DIURNAL RECORD 



221 



up in the middle of the day, each of the petals standing 

 erect. If the flower were susceptible to the stimulus of 

 gravity, then, on turning the flower upside down, the closed 

 petals in their inverted position would curl upwards and 

 outwards, thus opening the flower. But no such effect 



takes place. 



There remains only one other operative factor, namely, 

 that of variation of temperature, the characteristic effect 

 of which will next be demonstrated. 



The Thermonastic Recorder 



The apparatus is illustrated in fig. 128. One of the 

 perianth-leaves, N, of the Lily is attached to the short arm 

 of the lower recording lever. 

 The metallic thermometer T is 

 connected with the upper lever. 

 Simultaneous records can thus 

 be obtained of the diurnal 

 variation of temperature and 

 of the movement of the 

 petal. 



Experiment 125. Effect of 

 variation of temperature. — 

 Raising the temperature of the 

 chamber in which the flower 

 was placed induced a move- 

 ment of closure shown by the 

 down-curve (fig. 129). 



The Diurnal Record 



Fig. 129. Negative thermonastic 

 response of Nymphaea. 



Application of heat at the vertical 

 mark induced up-movement of 

 closure seen as a down-curve. 

 Successive dots at intervals of a 

 second. 



A continuous record of the 

 movement of the petal was 



obtained from 6 p.m. to 12 noon next day. The flower 

 was tightly closed from the forenoon, the perianth-leaves 

 beginning to open out in the evening, at first slowly, then 

 very rapidly ; the flower became fully expanded by 10 p.m. 



