IN THE MO roil ORGANS OF LEAVES. 



91 



d 



superior masses of parenchyma and the normal passive direction of the fibre 





vascular bundle to the fibro 



tissue of the secondary rachis. 



The fibro-vascular bundles issue obliquely from the bevelled surfaces on either 

 side of the upper half of the secondary rachis, and are originally di rooted forw uds 

 and slightly upwards from their sites of origin, and horizontally parallel to the lino of 



the 



rachis (Plate V, Fig. 5). Owing to the obliquity of origin of each bundle its upper 



surface looks upwards and forwards, and its lower one downwards and backwards so long 

 as the original position is maintained or resumed. The masses of parenchvnia lying 



one another in struct in e, 

 and are sharply defined from one another even where they arc not separated by the 



above and below the fibro-vascular band differ strikingly from 



bundle 



(Plate VI, Fig. 13). 



The 



superior mass is slightly 



thicker than its opponent. 



Its component cells have very thin walls and relatively abundant protoplasmic contents, 



and the tissue is comparatively an open one containing numerous, large, intercellular 



spaces 



have walls five or six times as thick as those of the superior one (Plate VI, 



the amount 

 The thiekm si 



in addition to minute angular ones. 



The cells of the inferior parenchyma 



Figs. 14 — 17), the tissue which they compose is a very dense 



of protoplasm which they contain is relatively trifling in amount. 



on o, an d 



of the cell-walls in the superior parenchyma is aobut 



0009 



in.ni. 



> 



that 



o 



f the 



in- 



ferior one about '0054 m.m. There is not any considerable difference in the amount 

 of chlorophyll content of tho two masses, but the upper one when in a condition of 

 compression, as it ordinarily is in the case of detached pulvini, 

 its opponent. 



appears greener 



tha 



The appear 



described above can be clearly made out in fresh sections in 



water or acetate of potash, but are much less distinct in permanently mounted sections, 

 unless these have been fixed by treatment with osmic acid ere exposing them to the 



action of other reagents. 



I 



•d 



t 



obtain p 



tissue as far as possible in a natural cond 

 cut sections ought to be 



of 



preparations representing the 



full 



dity, the freshly 



wed to be in water 



d to light for some 



time, so 



as to allow cond 



of 



dity under solar stimulation to he re-established, and 



then immersed for a few seconds in a 2 per cent, solution of osmic acid 



This 



treatment 



two 



ings 



fixation of the cell -walls to some 



fixation of the protopl 



contents of the cell-cavities. Unless it be adopted 



and, second 



the 



of the superior pad will certainly be more or less shrivelled 



d 



apsed, and 



most 



the cell-walls of the inferior one will lose the greater part of their thickness. r l 

 satisfactory permanent preparations are those which, after beim: stained with purocarmine 



are mounted in Farrant's solution; but even those 



ounted 



balsam are much more 



presentativ 



The 



g* 



manifestly con 



of common collenchv 



of the natural condit 

 part of the thickness 

 m posed 



of t 

 f the 



than any mounted without fi 



- 



walls in the inferior parenchyma is 



of materials resembling those in 



the 



tissues, and therefore normally 



ckened areas 

 ect to gr 



tho walls 

 reduction 



bulk on exposure to conditions leading to 



of water 



In unfixed 



which are subsequently exposed to immersion in absolute alcohol, &c, prior to mounting 



in 



balsam, a complet 



of 



of course, occurs 



> 



d with 



reduction in 



the thick 



of the cell-walls, and the same effect in somewhat minor 



degre 

 osmic 



occurs m 



unfixed sections 



ted in Farrant's solution; but treatment 



th 



acid allows of extraction of water without diminution in volume. If unfixed 



Eoy. Bar. Gard. Calcutta Vol. VI 



