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of these walls undergo lignification and occasionally suberisation as 
well. The radial and transverse walls are always both lignified and 
suberised, the former being pitted. Fig. 8 shows a transverse section 
taken from about the middle of the leaf. Some of the pericyclic cells 
have very thick, lignified walls, and a considerable amount of suberin 
is deposited in the walls of the tracheidal tissue, more than is the 
Fig. 8. Picea excelsa Link. Transverse section from the middle region of the 
leaf showing an uninterrupted endodermis. en., endodermis; s., suberin; 
lig., lignocellulose; c., cellulose. ( x 240.) 
case in Pinus. In Picea there is also a greater development of epidermal 
cuticle and of sclerenchymatous hypodermal tissue than in Pinus. 
This development of relatively impermeable tissue in the cortical 
region is especially noticeable at the base of the leaf where the endo- 
dermal sheath is incomplete. Here from 6-7 layers of sclerenchymatous 
hypodermal tissue are developed, while towards the middle of the 
