IN THE MOTOR ORGAN < OF LEAVK8. 



7 > 



open texture, whilst in Pithecohbium and Ltucwna thcv contained merely minute 

 nngular intercellular spaces like those of the superficial ones. Correal tiling with 

 these differences in the degree to which facilities for redistribution of fluid are present, 

 we find differences in regard to the rate at which movements arc mooted. The 

 leaves of Leucxna move more rapidly than those of PWiecohbium, but not 

 rapidly as those of Mimosa. When the temperature i high ami at mo 



so 



phone humidity low, 



a certain amount of depression of the secondary racl.isos and convergent elevation of 



the pinnules makes its appearance almost immediately after n leaf or shoot has bev.. 

 detached from the axis, and much sooner than m,y , m pending displacement ire visible 



of Pithecolob 



posed to similar conditions. This i„ j„ onv 1( . pi . ct re mask 



as the numbers of stomata in L.ucama are very mu.li smaller than in PHhmMn 

 In spite of this, however, ^inspiratory Joss takes place with ve.y great rapidity, p 

 bably in connection with the general delicacy of the tissues, as is indicated une,, ui- 

 vocably by the very early onset of phenomena of general wilting. As the atmosjfe ric 

 humidity rises, the rate of movement falls, and when a cond 



tion is present, movements are very greatly retarded so long as mechanical" disturl 

 ances of the leaves calculated to give rise to increased filtrativq discharge of fl 

 from the pulvinar tissues are absent. Jn Leuavna movements tendi 

 the establishment 



g sat ura 



g toward 



of the nocturnal position may, even more distinctly than in the 



as 

 <«ne 



cas9 of any of the leaves which have been previously described, be wcognis d 

 arising under the influence of many different conditions which only agree with 

 another in the fact that they all tend to induce diminished tar^ance in the 

 pulvinar tissues. In casss of separation of leaves or shoots from the a diminished 



tumescence arises in consequence of arrest -d supply and continued tnmspiratory loss 

 of fluid; where movements occur in connection with continued exposure t hot (by 

 air without separation from the axis, excess in ^inspiratory los-s acts alone; where thcv 

 follow much mechanical agitation, increased local filtration in the pulvinar tissu < comes 

 into play; and, finally, where they attend removal of solar stimulation, a fall in 

 osmotic capacity of the cell-sap is the determinant. Jn all ca. s alike, the loss of 

 strength, or, in other words, the diminution in tnrgescence falls most heavily upon 

 the younger and functionally most active masses of tissue, and consequently in all 

 alike, the movement which attends it is in the direction of the position which is 

 made for by the older masses of pulvinar tissues, because they are the structurally 

 stronger and functionally weaker ones. In certain cases the struggle is mainly be- 

 tween opposing mnsso fl of pulvinar parenchyma, whilst the vascular tissues are practically 

 passive; in others the vascular tissues co-operate with the older masses of pulvinar 

 parenchyma; and in still others they become the main determinants of the assumption 

 of the nocturnal position. In any case, however, the struggle is between functionally 

 powerful and structurally powerful tissues, the former constantly making for the 

 diurnal and the latter for the nocturnal position. The tissues which are distinguished 

 by structural strength neither undergo so much diurnal increase in tnrgeseenoe nor 

 provide such facilities for filtrative loss of fluid, as those which are characterised by 

 excess in functional strength; and consequently they are not subj< t to so much loss 

 of turgescence on removal of solar stimulation or on the incidence of conditions 

 calculated to give rise to increased filtration as the latter are; so that any deprivation 

 of light or increase in pressure on the pulvinar tissues must tend to give rise to an 

 assumption of the nocturnal position. Wlien we compare the rates at which 



emeu 



Ann. Roy. Bot. Gard Calcitia Vol. VI. 





