Plant cell and vascular tissueWatch
Where are they located. I am having difficulty imagining?
Do the plant cells surrounded the vascular bundles ?
The vascular bundles, as they are called, are placed differently in the stem than in the root. In the stem, they are placed as a ring of bundles in an incomplete circle a short way inside from the outer part [epithelium](in cross section) so in 3-D, they form an incomplete cylinder, rather like the tube of a pen. The teleological reason for this is that the main forces that the stem (being above ground) faces are horizontal (wind), and a tubular structure best resists such forces.
In the root, the xylem and phloem are present as a single group in the centre of the circular cross section i.e in 3-D, they are like a central rod. This is because the main force the root has to withstand is vertical as the root pushes downwards as it grows. A rod is the best shape to handle such forces.
Both the above arrangements follow from the fact that the vascular bundles are the stronger parts of the plant - one proviso: there are some variations in different species of plants depending on the habitat.
Hope this helps!
M (specialist biology tutor)