92 



THE CAUSES OF FLUCTUATIONS IN TUKGESCENCE 



alone are studied, there would appear to be little struct 



preparations 



unstability of position in the tertiary pulvini 



6 



d f 



or 



in fixed ones the 



ctural differences 



between the 



opposing 



masses of tissue are strikingly conspicuous 



The stru 



peculiarities of the tertiary pulvini thus present maximal facilities 



for the occurrence of 



cal displacement. There is an 



emely flattened fibro 



vascular bundle, and it is related above and below to large masses of tissue differing 



from one 



ther 



the highest 



degree in regard to 



their functional and structural 



gth. The tissue of the inferior parenchyma presents characters which imply the 



presence 



of 



y considerable and 



liability to functional alterations in turgidity 



ctural 

 So 



o 



th and of relatively little 



long as water is supplied to 



the collenchv 



material 



the cell-walls will secure absorpt 



maintenance of continuous structural resistance in high de 



5 



protopl 



n, and consequent 

 whilst the scanty 



content of the cell-cavities is little calculated to give rise to exten 



fluctuations in active functional turgescei 



diminution or interruption of water-supply, 



the tissue is likely to occur, because the fluid which is stored up within the substance of 



ice. On the occurrence of any sudden 

 no sudden diminution in the strength of 



the collenchymatous cell 

 it opposes an obstructic 



cannot be rapidly removed 



d 



long as it is present 



cavities, both as the result of the 



walls and the rigidity of texture which 



to the filtrative escape of any fluid from the interior of the 



?at thickness which it confers upon the cell- 



gr 



presence impl 



chyma of the tertiary pulvini, we have to deal with 



In the inferior paren 



for active turgescence of the protoplasts of the cell-cavities, but for 



turgescence of the cell 



The former 



a tissue providing not merely 



very considerable 

 a condition which is at once liable to 



elation to 



be affected by fluctuations in assimilatory activity; but the latter bears no direct 



unaltered so long as sufficient water-supply is present, 

 erefore, affected by the absence or presence of assimilatory activity, and 



and will remain 



It is n 

 remains 



constant 



feature of structural strength both diurnally and 



octurnally 







the other hand, the tissue of the superior parenchyma, with its relatively ooen texture 

 its very delicate cell-walls, and its abundant protopl 



arreat fluctuatio 



- 

 o 



f 



pid filtrative loss. 



latory turgescence, and also for 



provides the conditions for 



It 



th 



ch greater structural strength 



bundle to 



istantly opposed by a mass 



and by the inherent tendency of the "fibi 



occurrence of processes 

 f parenchyma of very 



resume its original position in relation to the 



circumstances which call its excess in functional 



quisite supply of fluid to satisfy th 



gth 



rachis, and it is only unde 



play and provide th 



sap as the result of assimilatory activity, that 



osmotic capacities which are developed 



the 



resistance to which it is 



must 



eak 



posed 



Any d 



epi 



in 



the struggle which it has to maintain, 

 nly dependent on active protoplasmic turgescence, whereas 



ipable of overcoming the 

 general assimilatory activity 



predominantly owing to mere physical properties of the 



rily be weakened 



because its 

 that of 

 walls 



gth 



is 





s 



pponent is 

 But it must also 





in the general 

 facilities v 



der the incidence of any influences giving rise to decrease 



pply of liquid or favouring filtrative loss because 



Inch it provides for redistribution of liquid in its relativel 



and the delicacy of th 



walls of its component cells 



the tertiary pulvini as motor apparatus 



a strictly 



reg 



periodic movements of 



are thus such 



of the structural 



open texture 

 The structural peculiarities of 

 to secure the occurrence of 



yctitropic character, and also to provide f 



