Lignification

... nutrients Phloem: Relatively soft -walled cells transport organic nutrients "Hardness and softness" is a function of the amount of lignification and extractive content of the individual cell walls not there location in the tree. Xylem: It is a dead complex permanent tissue. Sapwood ...

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... over time than the Metaxylem that forms later during a plant's growth. It is due to this that protoxylem has a narrower lumen due to excess lignification. As for their relative positions, it depends on the pattern of growth- whether it is centrifugal( as in stems where the growth starts ...

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