130 CUNNINGHAM ON FLUCTUATIONS IN TURGESCENCE. 



normal circumstances, acted fully as regards their primary petioles and pinnules, but showed hardly any 

 appreciable pinnal convergence. It was at once placed in a dark, moist chamber, which was allowed 

 to remain closed until 8-20. When the chamber was opened, the position of the various parts of 

 the leaves was found to be just the same as it was when they were enclosed in it. The shoot was 

 now removed from the chamber, laid on a table in front of a window and covered by a bell-o-lass. 



Within a short period the primary petioles gradually became partially elevated, and the pinnules 

 assumed the normal diurnal position almost completely. Two hours later the petioles remained as 

 before, but the pinnules had assumed a position intermediate between the normal diurnal and 

 nocturnal ones. According to the ordinarily accepted theory of the causation of the movements in 

 the leaves of Mimosa pudica, we are calied on in this instance to believe that the primary depression 

 of the petioles and elevation of the pinnules were dependent on stimulation and active contraction of 

 the protoplasts of the motor organs of the primary and tertiary pulvini incident on a factor — separation 

 from the axis — which failed to act as an appreciable stimulant to the protoplasts of the secondary 

 pulvini ; that this condition of stimulation and active contraction lasted continuously for nearly two 

 hours whilst the shoot remained in the dark and deprived of any solar stimulus ; that it was then 

 replaced by a condition of relaxation on exposure to the influence of light ; and, finally, that continued 

 exposure to light acted as a stimulant to the contractile protoplasts of the tertiary pulvini, but failed 

 to do so to those of the primary ones. It is surely more rational to explain the sequence of pheno- 

 mena in the following fashion. The primary depression of the petioles and elevation of the pinnules 

 were dependent on the sudden disturbance of liquid equilibrium throughout the tissues, caused by the 

 sudden arrest of root-supply of water and the active escape of liquid accompanying separation f 

 the axis. This depressive disturbance was sufficient to give rise to considerable filtrative discharge of 

 liquid, and consequent loss in turgescence, in those sites in which special structural facilities for the 

 escape of liquid from the interior of cell-cavities are present, and hence movements occurred connected 

 with sudden fall in tumescence in the inferior parenchyma of the primary pulvini and in the 

 superior parenchyma of the tertiary ones, whilst no appreciable movements occurred in the pinnae 

 because of the minor facilities for rapid redistribution of liquid provided by the tissues of the second- 

 ary pulvini. During the period in which the shoot was retained in the moist but dark chamber, 

 recovery of the diurnal position did not occur, not because there was not a stock of reserve water 

 within the water-conducting system, or on account of active transpiratory loss, which was precluded by 

 the atmospheric humidity of the chamber, but because the total absence of solar stimulation prevented 

 the protoplasts of the tissues from giving origin to the unstable assimilatory products on which the 



om 



osmotic capacity of the cell-sap, 



induce full turgescence of the tissue elements, 



was absent. ^ On subsequent exposure to sunlight, even under conditions implying no fresh supply 



transpiratory loss, the rise in osmotic capacity in the cell-sap 



stock of reserve water b 



permitt 

 was sufficient to determine active abso ption of the reserve water in the water-conducting system^d 

 therefore to determine a rise in the turgescence of the pulvinar tissues leading to a resumption of the 

 diurnal position of the primary petioles and the pinnules so long as enough reserve water remained 

 within the water-conducting ^system to more than counterbalance the coincident transpiratory loss. 



and assimilative decomposition of water) the 

 cy towards the resumption of the nocturnal 

 position set in and manifested itself earlier and more conspicuously in the pinnules than in the primary 

 petioles, because the action of local loss of turgescence in the tissues of the primary pulvini was more 



or less discounted by the coincident diminution in distal leverage attending diminished turgescence in 

 the lamiuar portions of the leaves. 



The effects of a normal depression cf assimilatory activity, or in other words of a normal 

 decrease in the osmotic capacity of the pulvinar tissues in giving rise to a greater liability to the 

 occurrence ot movements, or as it would be commonly described to « increased irritability," is very 

 strikingly demonstrated in connection with experiments, like the following, in which the tips of axes 



are gently amputated without any mechanical disturbance of the plants : 



^ Experiment II.— June 3rd. Both sail and air very humid. 

 position. A 



full diurnal 



nputation of the tips of axes was followed merely by the exudation of a great drop of 

 id from the cut surface. At 7 p.m. the leaves were in full nocturnal position. Amputation of 





