1X2 
PHARMACEUTICAL BOTANY 
already present on its inner face, the conveying of sap and storing 
of starch, etc. is gradually relegated to the outer wood layers, since 
Pig. 50. — Diagrammatic representation of a block of pine wood highly mag- 
nified. a, Early growth; b, late growth; c, intercellular space; d, bordered pit in 
tangential wall of late growth; m, f and e, bordered pit in radial wall of early 
growth from different points of view; h, row of medullary cells for carrying food; 
g, row of medullary ray cells for carrying water; k, thin place in radial wall of ray 
cells that carry food. (From Stevens.) 
the inner layers, step by step, lose their protoplasmic contents and 
power of conducting sap and become filled with extractive, resinous 
