84 



THE CAUSES OF FLUCTUATIONS US' TUKGESCEXCE 



The measurements in a section derived from another pulvinns were the following 



Vertical diameter of 



• • • 



• • • 



>5 



55 



>5 



5> 



55 



55 



55 



55 



55 



upper parenchyma 

 fibro -vascular axis 

 lower parenchyma 



- ■ • 



• • # 



• • • 



• • • 



• - • 



• • • 



159 m.m. 

 0-54 

 045 

 0-60 



v 



» 



of 



• • • 



55 



55 



55 



inferior 



• » 



Transverse diameter of the entire pulvmus 



5> 



55 



5* 



5» 



5? 



55 



55 



55 



55 



lateral parenchyma 

 fibro-vascular axis 

 lateral parenchyma 



0-0036 to 0-0054 



...0-0018 

 ... 177 



... 0-57 



... 0-63 



55 



55 



5? 



55 



55 



55 



• . • 



0-5 



*5 



These 



figures 



y clearly show the vertical comp 



of the pul 



a whole, and al 



excess in 



vertical compr 



of the fibro 



bundle 



as 

 the 



tal diameter exceeding the vertical one by 



10*8 per cent, in the former and 



by 22*6 per cent, in the 



This, 



however, is not 



the 



only 



difference between the opposed masses of 



parenchyma which make respectively for elevation and depression. Both are alike in 

 being composed of two distinct strata of tissue. The outer of these is relatively dense in 

 texture, the individual cells being separated from one another only by minute angular 

 intercellular spaces like those present in the pulvinar parenchyma of Pithecoiobium soman 



and Leuccena glauca, while the inner one is of very open 



character, being 



permeated 



throughout by a very extensive and highly developed system of huge intercellular spaces 

 (Plate VI, Figs. 3, 4, 12). The characters of the cell-walls also differ in the two strata. 

 In the outer one they are provided with numerous small pits like those in the walls 

 of the pulvinar cells of the other nyctitropic leaves which have been previously 

 described ; but in the inner one, in addition to such pits, they are provided with others 

 of a much more elaborate character and of much greater size. Tho latter pits have a 

 more or less circular or oval outline and a thickened rim, and are closed by a delicate 

 membrane which in its turn shows secondary pits or actual orifices of small size and 



these large pits appear to be 

 situated so as to abut on portions of neighbouring cells, but some of them appear to be 

 in direct relation to the great intercellular spaces of the tissue. The walls of the 



varied outline (Plate VI, Figs. 3, 4, 12). The majority of 



cells entering into the constitution of the outer 



trat 



um of tissue of the parenchyma lying 

 above the fibro-vascular bundle are about twice as thick as those of the corresponding 



stratum lying beneath it. 



The 



walls of the cells in 



the 



above and below the fibro-vascular axis do not differ fi 



rom one 



deeper strata both 



ler to any 



anotl 



of the pits. The cells throughout the entire thickness 



appreciable extent, and are alike of very considerable thickness save within the areas 



of the parenchyma both above and 

 below the bundle contain chlorophyll, but the numbers of chromatophores in the cells of 

 the deeper stratum of tissue are much greater than those in the superficial one, and this 

 implies a corresponding excess of chlorophyll in the inforior as compared with the superior 

 mass, seeing that the excess in thickness which the former 



an excess in the thickness in the deeper stratum of its tissue," the thickness of "the superfi- 



axis. The line of demar- 



presents is entirely owing to 



cial stratum being alike both above and below the fibro-vascular 



cation between the two strata of tissue is rendered very conspicuous, even under very low 



magnifying powers, in sections which have been momentarily immersed in a 2 per cent. 









