88 



THE CAUSES OF FLUCTUATIONS IS TUEGESCENCE 



filtrative escape of fluid from the inferior pulvinar tissues dependent on local increments 



of 



pr 



Such increments do 



of 



ffect the 



leverage 



of the 



distal portions of the leaf, but merely give rise to modifications in the relative strengths 

 of the opposed masses of pulvinar parenchyma of such a nature as to confer increased 



relative strength upon the superior one 

 a normal course and depression results. 



> 



and hence the movement of the petiole follows 



The 

 d muc 



dary pulvini differ structurally in many respects from the primary 



11101 



3 closely : 

 latter do. The fibro-vas 

 a solid cord devoid of any medullary 



esemble the pulvini of common nyctitropic leaves than the 

 (hilar axis, like that of the primary pulvinus, has the form of 



content, but it is only slightly flattened vertically, 



and therefore presents no special facilities for flexion 



one 



di 



another 



(Plate VI, Fig. 5a) 



The following figures show the measurements of the various poi 



of 



derived from distinct pulvin 



line of 



first case having 



fallen parallel with the length of the fibro-vascular bundle (Plate VI, Fig 



7 



and 



in the second at light 



(Plate VI, Fig 



Section 1 . — Total breadth of pulvinus 

 Breadth of external mass of parenchyma 



„ fibro-vascular bundle 



„ axillary mass of parenchyma 



• • • 



• • • 



1-005 m.m 



• • • 



i • • 



• • 



0-33 

 0-33 



0-345 



1-08 



0-33 



0-39 

 0-36 



Thickness of cell-walls on the outer mass of parenchyma O'OOIS to 0*0036 



„ of cell-walls iu axillary mass of parenchyma 0*0018 to 0*0027 



111 



0-39 

 0-33 



0-80 



» 



>* 



5> 



Section 2. — Transverse diameter of entire pulvinus ... 



„ „ of outer parenchyma 



„ „ of fibro-vascular bundle 



„ „ of axillary parenchyma 



55 



5? 



» 



55 



JJ 



55 



Yertical diameter of entire pulvinus 



55 



55 



55 



55 



55 



5) 



)•> 



superior parenchyma 

 fibro-vascular bundle 

 inferior parenchyma 



55 



• • . 



55 



• • • 



• • • 



tj 



These figures show that the fibio-vascular bundle 



more rounded th 



prim aiy pulvin us 

 every direction ; 



aud relatively strong in 



relation to the 



and also that the pulvinus as a whole, in 



surrounding parenchyma 



of being flattened 



vertically, is somewhat compressed laterally. The horizontal diameter of the fibro 

 bundle sometimes, as in the second section, slightly exceeds that of either of the lateral 

 masses of parenchyma and, in other cases, falls slightly short of that of the inner one, 

 as in the first section. The walls of the cells in the outer mass of parenchyma are some- 



what thicker than they are in the ~.. 

 this respect is present here as in the 



y one, but 



of 



conspic 



difference in 



parenchyma of the primary pulvinus. The tissue of the internal 



cell-walls in the superior and infer 



slightly richer in 



•phyll than that of the outer 



presence of two structurally distinct layers in the thickn 



one. There is no 



axillary mass is 



dence of 



darkens uniformly down to the bundle-sheath under treatment with some 



of the parenchyma 



It 



absence of any great system of intercellular 



• 1, and 



spaces like that in tho deep 



stratum in the parenchyma of the primary pulvinus. A certain number of cells 



with large and elaborate pits is, howe\ 

 bundle-sheath; but these cells do 

 distributed 



pro 



vided 



form 



present m the immediate neighbourhood of the 



continuous layer, and they 



The only features, then, which distinguish the axillary from the outer 



'r> 



larly 



mass 



i 



