Why vascular bundles of dicot stem are described as conjoint, collateral and open?

Describe the T.S. of dicot stem.

Why concentric vascular bundles are always closed?

The transverse section of a plant material shows the following anatomical features, (a) the vascular bundles are conjoint, scattered and surrounded by sclerenchymatous bundle sheaths (b) phloem parenchyma is absent. What will you identify it as?

Concentric vascular bundles are always closed. Describe.

Which type of vascular bundles are observed in isobilateral leaf?

A section of the stem had vascular bundles, where tissue was wrapped around the other. How will you technically describe it?

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