Q.While observing a section many scattered vascular bundles could be seen. Teacher opined that in spite of this large number the stem cannot grow in girth. Why?

A representative monocot stem (e.g. maize) abandons a dicot stem's careful three-way cortical zoning almost entirely. Its hypodermis is sclerenchymatous rather than collenchymatous, since there is no ongoing elongation phase to accommodate with flexible support - rigid support is laid down immediately instead. Its ground tissue is not differentiated into cortex, endodermis, pericycle and pith at all; it remains one continuous mass of parenchyma from just beneath the hypodermis to the stem's centre, so there is consequently no starch sheath and no medullary rays, since neither a true endodermis nor a ring of separated bundles exists to define them. The vascular bundles are conjoint and collateral like a dicot stem's, but closed - no cambium sits between xylem and phloem - and rather than forming a single ring around a pith, they lie scattered through the ground tissue with no consistent radial pattern, e …