74 



THE CAUSES OF FLUCTUATIONS IN TUBGESCESCE 



dary pulvini of Mimosa pudica, the masses 



of pulvinar parenchyma surrounding it 



either equal 



exceed 



ickness; whe 



dary pulvini of Pithecolob 



mmon 



it takes the form of a 



flattened hand, the superior and 



diameter, and. the lateral ones falling 



inferior masses exceed 

 short of it in horizontal diameter; but 



m 



the 



ondary pulvini of Leuccena glauc 



the thickness of the axial mass of vascular 



edullary tissue 



every direction. (Plate III, Figs. 8, 9 



of 



and n 

 parenchyma in 



In the cas 

 disposed above 



are not simple movements of dep 

 nules of Pithecolob 



siderably exceeds that of the 



ounding masses of pulv 



tertiary pulvini the opposin 



of pulvinar parenchyma are 



d beneath the 



but the movements which they determine 



and 



like those prese 



the 



pm 



This is owins: 



o 



the following facts 



In the first 



the pul\ 



ibliquely 



upon 



bevelled surface, so that the opposed 



masses 



directed respectively upwards and forwards and downward 



and backwards, just as 



they 



are 



in the tertiary pulvini of 



M 



pudi 



(Plate V, Fig. 5); and 



second place, they hold a 



elation to the lamina of the pinnule 



ery 



sun 



the 

 to 



that which 



pres 



of the pinnae of Cass 



alata. 



The oblique disposi 



of the opposing p 



masses 



ly implies that the upper one must make 

 but also for backward displacement of the lamina, and the 



ranee. So far, of course, 



not merely for depression, 



under one not merely for elevation, but for elevation and ad 



we 



dealing with movements of dep 



and ele 



on an oblique 



face, but 



character of the movement is further modified by the unlike 



which the mass 



of pulvinar parenchyma bear to the two halves of the lamina. There are conspicuous 



pansions 



of pulvinar tissue involving the base of the 



poster 



or 



half of the 



lamina both on its superior and inferior 

 course, must tend respectively to deter 



ipects (Plate III, Fig. 10), and these, of 

 ne rotation outwards and inwards of the 



upper surface of the 

 and resistance. The 'inf 



midrib according to the variations 



in their relative strengtl 



and elevat 



pulvinar pad consequently not only makes for general 



of the 



advance 

 and when 



keel of the midrib comes to lie sup 

 nule. The ultimate 



but for excessive elevation of its outer half 



oped nocturnal position, the pi 



the displacement has advanced so far that the posterior side of the 



deflection of the pin- 



the fully devel- 



the anterior 



de, to 



of the conditions is that when the leaf 



only have their upper surfaces £ 



directly 



wards, but slope downwards and forwards from the plane of the petiole. An 



the 



relative strength of the upper mass of pulvinar parenchyma 



r 



depressive div 



and 



ersely not only 



half of the lamina, and 

 surface of the midrib, in pi 



trocession, but also to special dey 



o 



t 



outer 



consequently 



f fac 



o 



urface of the lamina lies in the same pi 



ation of the vascular axis, so that the upper 

 inwards, faces directly upwards, and the upper 



with and more or less at 



secondary rachis. There is not any very conspicuous difference in the 



£> 



thickness of 



cell-walls of the opposing masses of 



but the 



derably richer in chlorophyll corpuscles than the inferior one is 



super 



t angles to 

 rength and 

 one is con- 



The pulvinar tissues in Leucama glauca are even more extensively and conspicuously 



pitted than those of Pithecolobium saman 



but they 



ble the latter, and diff 



from those of the primary pulvini of i Mimosa pudica 



being throu 



o 



his 

 hich 



spaces (Plate VII, Figs. 3 



devoid 



4, 5). 



any highly developed system of intercellular 

 is specially conspicuous in regard to the primary pulvini of the deeper strata 



Mimosa pudica are not merely very, extensively pitted, but 



are 



of 



tremely 







