IN THE MOTOR ORGANS OF LEAVES. 



-7 



turgescence of the inferior parenchyma sustained in spite of excessive local facilities for 

 rapid filtrative escape of fluid and the combined compressant action of the superior paren- 

 chyma and distal leverage, so that anything giving rise to sudden loss of osmotic pro- 

 perty in the cell-sap, to sudden diminution in the supply of fluid to satisfy the osmoth 

 capacity of the latter, or to sudden increase in the conditions of local pressure affecting 

 filtration must inevitably lead to sudden movements. Active turgescenco of the ex. live- 

 ly porous tissue of the deeper stratum of pulvinar parenchyma can only he maintain* I 

 as the result of the continuous addition of highly osmotic and unstable a^imilat>ry pro- 

 ducts to the cell-sap with coincident abundant supply of fluid to make good the constant 



tiltrative loss which is going on in the tissue; 



and it is only under conditions of high 



turgescence that the inferior mass of pulvinar parenchyma is able to overcome the •on- 

 joint action of the superior mass and of distal leverage so long as tho latter is main- 

 tained at a high level. The superior mass of parenchyma is not devoid of tissue pre 

 senting special facilities for rapid redistribution of fluid, but it contains much less of such 

 tissue than the superior one does, and hence any 



conditions determining general loss i 



n 



turgescence must produce greater and more rapid weakening of tho inferior than of the 



of strength in the 



superior mass 



superior mass. Under ordinary circumstances the loss 

 is thus concealed by the greater loss taking place in tho inferior one, and it is onl\ 

 where the action of any agent inducing a fall in turgescence is carefully limited to the 

 superior mass that we have any indices to its action upon it (vide Appendix B). 



The structural peculiarities permitting of the occurrence of rapid loss in turgescence in 

 the inferior mass of pulvinar tissue also permit of rapid gain, processes of rapid endos- 

 mose being provided for by tho excessively porous character of the cell-walls and the 

 abundant chlorophyll contents of the deeper stratum of tissue. Tho process of elevation is, 

 of course, never so rapid as that of depression, because it is resisted by di>tai leverage, 

 and is mainly carried out by osmosis in place of filtration; but in spite of this it is 

 very much more rapidly conducted than it is in cases where the pulvinar tissues do not 

 provide the same facilities for rapid absorption of fluid, and under favourable circum- 

 stances of illumination and water-supply, its progress is readily visible to the unaided 

 eye (vide Appendix B). 



The structural peculiarities of the inferior masses of pul 

 primary pulvini of Mimosa pudica unequivocally provide facilities for the 



parenchy 



m 



\ in the 

 f sudden 



loss of turg 



,bly suddenly 



the tissue, but the 

 cuted. The capacity i 



movem 



in the primary petioles are not 



f sudden movements i^ 



occurrence 



dependent 

 of fluid i 



the presence of 



structural peculiarities facilitating rapid movem 



the 



but 



actual occur 



of 



dden movements, even in cas - 



eh peculiarities are present 



very high degree, depends on the sudden in* 



Hence in Mimosa pudica 



where si 



cidence of conditions making for the redistribution of fluid 



any gradual diminution in water-supply only causes gradual movements in the primary pe 



in spite of the 



tural f 



for escape of fluid from 



motor organs; and, further than this, the effects of gradual local 



tissues of their 



tur- 



10ns 



g 



leverag 



m 



so 



the 



may be 



than discounted by 



cident alterations in distal 



that elevation in place of dep 



may occur. It is only und< r such cir- 



cumstances, however, that movements of this rever d character are present : 

 with loss of strength in tho inferior as compared with the superior pul 



paren 



chyma 



They never occur in 



connection with conditions implying local increase in 



