What is the circular tube in the middle of a carrot? Why is it there/what does it do?
Sparing no expense, I sliced a thin section of carrot and examined it under my microscope - the core appears to be composed of vertically aligned fibres/tubes, the outer layer seems to be radially arranged.
My hypothesis: The core is the equivalent of the xylem layer in a tree, containing the vessels that transport nutrients and water to/from the leaves/roots. The outer layer being for storage.
As I said, this is a hypothesis (although hardly a ground-breaking one), but is further borne out by the fact that the core connects directly to the basal rosette from which all of the leaf-stems arise.
I sure wish folks would go to that much trouble for my questions
Mangetout’s essentially right. Carrots are tap roots, and in that type of root system the central region enclosed by the endodermis includes phloem cells which carry food produced in the leaves to the rest of the plant, as well as the tubular xylem which transport water and minerals from the root up to the leaves. Outside that is the cortex which stores the plant’s food.
This explains it reasonably well (PDF file).