128 



CUNNINGHAM ON FLUCTUATIONS IN TUEGESCENCE. 



chamber the nocturnal 



again resumed, and was once more 



the diurnal one on 



return to the chamber. Tho phenomena present in this experiment not only demonstrate the extreme 



which coincides with minor degrees 



turgescen 



rapidity of transpiratory loss and the accuracy of the balance which must be maintained between 

 transpiratory loss and root-supply of water in order to the retention of a given position by the pinnules, 

 but also that the nocturnal position is one 

 motor organs, and not with increased turgescence a& affirmed by Pfeffer. 



The results of six experiments with -regard to the actual amount i 

 under favourable circumstances were as follows : 



Experiment II.— A plant with seven leaves and 222 pinnules yielded 231 C.C. of water in 



twenty -four hours. 



Experiment III.— A plant with 



3*40 C.C. water in twenty-five hours. 



4'32 grammes yielded 



Experiment IV 



■gfc 



Experiment V.— A plant weighing 2*03 grammes yielded 4*1 C.C. water in twenty-four hours. 

 Experiment VI. — A plant with five leaves and 194 pinnules and weighing 2 32 grammes yielded 



1*5 C.C. water in four hours. 



The following experiment illustrates the results following a disturbance of the norm 

 between transpiratory loss and root-supply of water: 



balance 



Exp 



VII 



into the ground were cut off. 



The protruding portions of the roots of several pot-plants which had rooted 



In some of the plants the branches were cut shoit, so as to leave only 



a limited number of leaves; in others they were left intact. Thirty -six hours later all the leaves on the 

 plants with shortened branches were in full diurnal position, whilst in the plants with intact branches 

 the pinnules were in a position intermediate between the diurnal and 

 thing to account for the difference in the 



noctun 



The 



rence in the position of the pinnules in the two sets of plants is that in 

 the case of those with shortened branches the transpiratory surfaces had been reduced coincidently with 



in those with intact branches the apparatus for absorption had been 



the 



absorptive ones, whereas 



dished, whilst that determining loss of water remained as bei 

 The next experiment also illustrates the effects attending 



b 



the 



supply and loss of water, only in it the absorptive surface was an abnormal one, 



& 



i 



b 



o 



Experiment VIII. — A detached shoot was 



that its lower extremity dipped into 



a vessel of water and was exposed to diffused sunlight. At 11-23 a.m. the pinnules were all almost in 

 full diurnal position. The water- vessel was now carefully removed without in any way disturbing the 

 shoot, and at 12-7 noon the pirn 

 replaced and a fresh absorptive 



h 



elevated. The water-vessel was now 



ive surface provided by subaqueous division of the lower end of the axis, 

 and at 2-20 p.m. the pinnules had almost all regained the normal diurnal position. 



The results in experiments like the two preceding ones are precisely parallel to those attending 



exposure 



hot 



but 



]n order to establish a tendency towards the assumption of the nocturnal position all that is necessary 

 is that the pre-existent equilibrium between supply and loss of water should be disturbed in such a 



iashion as to cause the latter to undergo a relative increase. Such 



increase may arise either as 



the result of diminished supply or of increased loss, but in any case the effects which it produces are 

 the same. In the case of normally rooted plants an excess of loss may arise in consequence of 

 excessive aridity and temperature of the atmosphere such as frequently prevails at midday and during 

 the course of the afternoon, and hence under such circumstanoes a spontaneous assumption of the 

 nocturnal position frequently manifests itself in spite of the fullest solar stimulation of assimilatory 

 activity. In the case of plants with partially ex] 



osed 



of 



ached 



similar diurnal 



assumption of the nocturnal position attends any sudden arrest or considerable diminution 



of water even when conditions are unfavourable to th 



upply 



In the f 



occurrence of excessive transpiratory loss. 



case recovery of the normal diurnal position attends a diminution in transpiratory loss; 



" water-supply, conditions of transpiratory loss remaining unaltered. 



either case which determines the resumption of the normal diurnal 



the renewal of 



It is relative diminution in loss in 







