Identify from the following, a plant tissue in which lignin does not occur in the cell walls?

A mature sieve tube differs from vessel in

Distinguish between the following : Protoxylem and metaxylem

The difference in phloem of gymnosperms and angiosperms is due to

Thick-walled and lignified with simple pits in walls and non-prosenchymatous cells without living protoplasm usually isodiametric or irregular in shape are

All xylem elements when mature are dead except