STD 11 - 13. Plant growth and development — BIOLOGY STD 11 Science — Question

c
(c) : The protoxylem differentiates in the parts of the primary body that have not completed their growth and differentiation. In fact in the shoot, the protoxylem matures among actively elongating tissues and is, therefore subjected to stresses. In the root, the protoxylem elements persist longer because here they mature beyond the region of maximum growth. In this differentiation annular and spiral thickening take place.