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section as a thin layer surrounded by a lignified wall on either side. 
In very few cases were the pits cut in such a direction as to exhibit 
the break in the lignified wall. The radial walls were found to consist 
of a central core of lignocellulose with a thin layer of suberin on either 
side. The presence of this thin suberised layer can be demonstrated 
by staining with Sudan III or alkannin, when it takes a deep red 
colour; or by soaking the sections in eau de Javelle for twenty-foui 
hours, adding phloroglucin, and mounting in hydrochloric acid, when 
the main central part of the radial longitudinal wall appears yellow 
whilst a pink line is produced on either side of the cut surface of the 
wall owing to the presence of the thin suberised layer (Fig. 2, b). 
The central core of the wall is strongly carbonised by sulphuric acid 
and does not stain with such reagents as alkannin and Sudan III. 
The suberised layer is generally continued round the corners of the 
cells towards the tangential walls, particularly so in the case of the 
outer tangential wall. Numerous simple pits are present in the radial 
walls (Fig. 2, c). The pit membrane is of cellulose. 
The tangential walls consist largely of lignocellulose, but both 
inner and outer walls have deposits of suberin on their inner sides, 
though these are not continuous over the whole surface (Fig. 2, d ), 
patches of unsuberised wall being left here and there. Pits on the 
inner tangential walls can be seen clearly if the sections are treated 
with eau de Javelle followed by dilute sulphuric acid. The pits are 
simple ones communicating with the parenchymatous cells of the 
pericycle. The latter in their turn are possessed of simple pits where 
they abut on other parenchymatous pericyclic cells, but pits are 
absent where they abut on tracheidal tissue (Fig. 3). The transfusion 
tracheids alone have bordered pits. 
The transverse walls of the cell are unpitted and resemble the 
radial walls in structure, though they are thinner than these. A 
central core of lignocellulose is present, covered on either side with 
a thin layer of suberin. Along a central line running across the wall 
in a radial direction the wall appears thin and it readily breaks here 
in sections of the leaf (Fig. 2, b ). 
Thus, in the endodermis of the fascicular leaves of Pinus sylvestris 
the radial and transverse walls are completely lignified and suberised, 
while the tangential walls are lignified and suberised in patches only. 
In no case were any of the endodermal cells in the adult leaf found 
to consist of unchanged cellulose, and no passage cells were observed. 
The action of alkannin and of Sudan III shows that the tracheidal 
tissue is suberised to a certain extent, and this is further borne out 
