Structure and Function of Endodermis in Abietinece 273 
cellulose is present. There is considerable development of transfusion 
tracheids in the leaf. 
( c) The fascicular leaves. 
These are semi-elliptical in section, growing in pairs in a sheathing 
investment of membranous scales. Stomata are present on both sides 
of the leaf. The epidermis is cuticularised and a lignified hypodermal 
Fig. 2. Pinus sylvestris L. (a) Transverse section of primary leaf. Radial walls 
of endodermis lignified in the middle and suberised at the edges. ( b ) The 
endodermal cells of a mature leaf as seen in tangential longitudinal section 
after treatment with eau de Javelle followed by phloroglucin and hydro¬ 
chloric acid. Both radial and transverse walls consist of a lignocellulose 
core enclosed by a layer of suberin. The radial walls are interrupted by 
cellulose pits. ( c) A piece of the radial wall stained with phloroglucin and 
mounted in hydrochloric acid. The wall is shown in surface view. Simple 
unthickened pits are present. ( d ) The endodermis of an old leaf in trans¬ 
verse section after treatment with eau de Javelle followed by phloroglucin 
and hydrochloric acid. The distribution of suberin on the radial and 
tangential walls is shown, en., endodermis; lig., lignocellulose; s., suberin; 
Y.I., radial wall; r.t., transverse walls; s.p., simple pit; c., cellulose; per., 
pericycle. ( x 240.) 
layer is present which is doubled along almost the whole of its length 
in old leaves. The adult leaf shows a well-developed regular endodermal 
sheath, the cells of which (Fig. 2, d) have all their walls thickened, 
the radial walls being suberised and the tangential walls lignified. 
The tracheidal tissue shows bordered pits which usually appear in 
