Structure and Function of Endodermis in Abietinece 281 
bordered pits. The bundle is undivided in the cotyledon, but is 
usually separated into two in the mature leaf. 
A transverse section of the base of an adult leaf shows the endo¬ 
dermis as an irregular layer of cells which cannot be traced continu¬ 
ously round the bundles (Fig. 7). The thickening of the walls of the 
endodermis varies in character. A few cells were found in which the 
walls were entirely dissolved by the action of concentrated sulphuric 
acid. 
Fig. 7. Picea excelsa Link. Transverse section from the basal region of the 
leaf showing the incomplete endodermis. en., endodermis; pal., palisade 
tissue; per., pericycle. ( x 240.) 
The radial walls, in most cases, have a lignified core with suberised 
layers on the surface and numerous pits. Usually both inner and 
outer tangential walls are lignified and may in addition be suberised 
over part of their surfaces. 
Towards the middle of the length of the leaf a continuous sheath 
of thickened endodermal cells is present; this sheath dies out just 
before the tip of the leaf is reached. The tangential walls are in many 
cases of cellulose and readily dissolve in sulphuric acid, though parts 
Phyt. xxi. v. 
19 
