58 



THE CAUSES OF FLUCTUATIONS IN TUEGESCENCE 



The pulvh 



L 



vary with the structural facilities provided for filtration 



fflmica, and especially in Mimosa pudica, provide great facilities for filtration ; their pulvina 



turgescence 



is consequently 



7 



unstable, and movements are very readily induced in 



whilst in Cassia alata the tissues provide minor facilities, and must be subjected 



to frequently recurring increments of external pressure befoi 



a 



suffi 



filtrative 



displacement h 



red 



alterations in turgescence of suffi 



gnitud 



to 



lead to appreciable alterations in the relative po 



of the various parts of the 



leaves. 



# 



Parallel phenomena present themse 



where the tissues, in place of being 



:posed to conditions tending to give rise to increased filtration, have their normal water- 

 pply interfered with. If a shoot of Leucama ghuca or Mimosa pudica be gently 



on likely to induce 



detached from the axis with a 



eful avoidance of all agitat 



increased pulvinar pressure and consequent augmented filtrative loss, the precaution does 

 not under normal circumstances prevent the leaves from manifesting movements, very 

 rapidly in the former and almost immediately in the latter case ; 



whereas 



movements make 



appearance 



ly very gradually, and after the lapse of 



Cassia alata 

 a consider- 



able interval. In all cases the deprivation of .water-supply under such circumstances is 



i 



alike, but the rate of movement subsequent to its inciden 



according to the activity 



with which filtrative processes are normally carried on by the pulvinar tissues. 



of L 



The 



glauca and 



filtration which is constantly going on in the pulvinar tissues 



Mimosa pudica under normal circumstances is more rapid than in those of Cassia alata ; 



>scence of the tissues in 



and consequently when the water-supply 



off the turg 



the former cases falls more rapidly than it does in the latter 



The degree of turg 



in any mass of tissue at 



given 



must 



iy 



depend on its osmotic capacity and on the supply and filtrative loss of fluid to which 



it is 



bjected. The condition is one of unstable equilibrium, and the degree of insta 



bility must necessarily be related to the deg 

 present. 



which inherent filtrative fac 



are 



Wl 



any increase ra 



these are present in high degree, any diminution in osmotic 



dit 



of 



nal 



power 



lable for absorpt 



pressure, or any arrest in the supply of fluid 

 will give rise to proportionately rapid loss in turgescence. 



Where, on the other hand, they are low, the loss must 

 delayed. Turgescence implies a balance between certain 



ecessarily be correspondingly 

 conditions of osmotic gain and 



or increase in the latter must 

 Decreased absorpt 



may 



arise 



filtrative loss of fluid, and any decrease in the formei 

 necessarily tend to give rise to diminished turgescence. 



either as the result^ of decreased osmotic property or of decrease in the" amount of fluid 

 available for absorption, and increased filtration must tend to arise under the influence of 

 any augmentation of external pressure. The structural facilities for filtration, however, 



consequently the alterations in turgescence which actually take place 



remain 



and 



under the influence of any alterat 

 exposed must necessarily differ 

 which they are cj 

 peculiarities of the affected tissue 



in th 



conditions 



to which a mass of tissue is 



in different instances, their magnitude and the rate at 



pable of inducing appreciable movements varying with the structural 



from 



bnt such increased loss cannot be the essential determinant of the alterations in tumescence of the motor organs alluded to 

 above as we find the assumphontf the nocturnal position occurring equally readily where the wind k accompanied by ] 



agitation 



eavy 



