A growing root tip

A root tip is the clearest place in a whole plant to see the difference this chapter turns on — and the first part of it you can see without a microscope at all.

Activity 1.2

Take the growing tip of an aerial root of nuga, or a prop root of wetakeyiya, or a prop root of rampe.
Observe its external appearance.
Use a hand lens for this.

Figure to be added

Figure 1.2 — the external appearance of roots: a cluster of thick hanging aerial roots, and a bunch of prop roots with their pale growing tips.

What you can see with a hand lens

The growing region is soft and pale in colour. The mature part behind it is darker and stiff. Nothing has been added to the root to make the older part firm — the same root is soft at one end and hard a centimetre further back.

What is inside, and why

The reason lies in the tissues the two regions are made of. Cut the tip lengthways and look at it under a microscope, and the two regions are as different inside as they felt outside.

Figure to be added

Figure 1.3 — a longitudinal section of a root tip under the microscope, with the root cap at the bottom, a line A to A dash across the region just above it, and a line B to B dash across the region further up.

Region A — A′

Cells that are dividing constantly, all much alike, all small. This is where the root is being lengthened.

Region B — B′

Several different kinds of cell, noticeably different in form from those in A. These have stopped dividing and taken up jobs.

The difference you can feel is a difference in what the cells are doing

Soft and pale means cells that are still dividing and have not yet become anything. Dark and stiff means cells that have finished dividing and specialised. Every plant tissue in this chapter falls on one side of that line or the other, and the next page gives the two sides their names.