APPENDICES. 



137 



amount of pmnular elevate was recognisable. After an exposure of thirty-two minute, the pinnules 

 occupied a position more or less intermediate between their normal maximal diurnal and nocturnal 

 positions. No perceptible alteration in the positions of the primary petiole occurred throughout the 



entire course of the experiment. 



Experiment IX.-No immediate effect followed transfer to the dark-room. After dti exposure 

 of thirty minutes the pinnules occupied a position almost intermediate between the maximal diurnal 

 and nocturnal positions: at the close of an hour the pinn* and pinnules were almost in maximal 

 normal nocturnal position, but the primary petioles remained elevated. 



Eepeated experiments of a like nature unequivocally showed that mere deprivation of light 

 however sudden and complete it be, is never an efficient factor in giving rise to the occurrence of 



sudden movements, and that it is in itself unattended by the occurrence of deep petiolar depression 

 even where it has acted during periods prolonged enough to secure maximal convergence of the nimrt 

 and elevation of the pinnules. They further ahowed that elevation of the pinnules occurs somewhat 

 more rapidly in plants exposed to a dry atmosphere than in those exposed to a humid one, and, conversely, 

 that recovery of the diurnal position on renewed exposure to light occurs more rapidly iu a humid 

 than in a dry atmosphere. 



In the case of experiments of this nature we have to deal with movements connected with the 

 incidence of external influences determining fluctuations in the functional activities of the tissues of the 

 motor organs, but the fluctuations are of a negative not of a positive nature ; they are dependent, not on 

 the incidence, but on the removal of stimulation, and the decrease in turgescence of the tissues of the motor 

 organs which directly determines the displacements of the various parts of the leaves is caused, 

 not by active contraction of the protoplasts of the tissue elements, but by the elastic recoil of the 

 cell-walls, which is no longer efficiently opposed owing to the decreased osmotic property of the cell-sap. 

 The movements are of a slow and insensibly progressive character, as is the case with all movements arising 

 under similar circumstances. In all cases in which the occurrence of movements tending towards the 

 assumption of the nocturnal position in the leaves of Mimosa pudica can be unequivocally traced to 

 alterations in protoplasmic functional activity acting alone, the displacement is invariably of a slow 

 gradually progressive character, and in all cases it is connected not with stimulation, but with depression 

 of protoplasmic activity. Sudden exposure to absolute darkness implies sudden deprivation of solar stimu- 

 lation of the protoplasts of the tissues, and with this a sudden depression of assimilatory activity ; but the 

 effects of this do not manifest themselves suddenly, because assimilatory activity is only indirectly related 

 to the maintenance of maximal turgescence through the intervention of the osmotic properties which it 

 confers upon the cell-sap owing to the products which it adds to it. The deprivation of solar stimulation 

 places an arrest on the assimilatory addition of osmotic products to the cell-sap, but the actual loss in 

 turgescence ultimately ensuing on this will be regulated by the progress of expenditure of the osmotic 

 products present at the time at which the arrest took place. The deprivation of the conditions securing 

 maintenance of turgescence at a certain standard is sudden ; but the fall in turgescence is gradual, 

 because it is connected with the gradual expenditure of a stock of pre-existent unstable materials. So, 

 in the case of plants which are exposed to the influence of the vapour of chloroform in a bumid 

 atmosphere, gradual progressive movements alone occur, because here again we have to deal only with 

 depression and ultimate abolition of assimilatory activity leading to loss of osmotic capacity of the cell 

 sap, and through this to alterations in the turgescence of the tissue-elements. But, whilst depression 

 of functional activity is incapable when acting alone to give rite to the occurrence of sudden move- 

 ments, it may serve to seoure their occurrence when it co-operates with other conditions favouring 

 losses in turgescence, but equally incapable of inducing the occurrence of sudden movements when acting 

 alone. The sudden introduction of a plant into a desiccated atmosphere is, as a rule, followed merely 

 by very slow progressive movements of the pinuules, or, in cases where the root-supply of water is 

 very abundant, may be unattended by any movements whatever; but sudden introduction into a chamber 

 containing both sulphuric acid and chloroform is normally followed by the occurrence of sudden rapidly 

 executed movements, because here we have to deal not merely with conditions depressing functional 

 activity or giving rise to great increase in tianspiratory loss, but with conditions implying the coiuci- 

 dent presence of both these factors of decrease in turgescence. Are we to suppose, as the ordinarily 



