Inside plant roots – an introduction
David Beeson, February 2021
You would be advised to see the articles on stems and leaves first.
Seldom seen, but roots are useful plant components!
Most people first come across in the form of carrots, parsnips and swedes. These are food-storing tap roots, while most roots are fine and spreading – netted or fibrous root systems. Both styles function in anchoring the plant, taking in water and soluble minerals (nutrients, mineral salts). A modern botanist would add: communicating with adjacent plants, producing hormones and interacting with fungi. Of course, roots will also store useful resources, and move materials up and down from the aerial parts of the plant.
We saw previously that young* stems have their transport (vascular) tissues towards the outer edge. This copes well with side forces from wind. Roots care little about side forces, but care greatly about forces attempting to pull the plant out of the ground – their vascular tissues are mostly central.
*Always start plant anatomy with young (primary) structures, as they are easier to understand, and you can observe the whole cross section (TS or transverse section) under a microscope. Older developments are secondary structures or tissues.
Sunflower (Helianthus) primary root centre
Px = primary xylem, a = primary phloem, with the ring of cells the endodermis
Look for those components below, and you will also see a side (lateral) root developing. The cortex is beyond the endodermis.
As before, red stain = lignified tissue, in this situation xylem for water transport.
Green-stained cells are non-lignified and those within the endodermis include the food transporting phloem tissues.
Above: You should still be able to spot the large, central xylem in a cross and clusters of small phloem cells between the arms. The cortex (showing starch grains inside) is composed of large cells that could be storing materials and there will be an epidermis around it all to offer some protection.
Root hairs are short-lived single cells that grow out of the epidermis.
My plant anatomy reference book is: Plant Anatomy, an applied approach by Cutler, Botha and Stevenson. It may only be available second-hand.
PS I did not have great specimens in my own collection, so have had to borrow! They are not showing as clearly as I would wish … but you can find them on the Internet in better detail.
NOTE: over 90 articles available, free of adverts. See: nwhwildlife.org – Rocky Mountains, USA and Index.