Erica's Original Notes Three-quarters of a plant are invisible, growing underground in the form of roots.Their growing tips are protected by special cells, exuding a mucilage, and thus acting as a lubricant. Absorption of the film of water that is in the soil occurs behind the growing tip. The roots often intermingle with roots of other plants and feed each other; cut trees may be powered by others left standing.
There are two sorts of roots: a) fibrous, e.g. grasses, and b) tap, e.g. carrots. (See 1 below.)
Uses for Roots: a) They act as an anchor. b) They absorb water and minerals (large trees absorb as much as 300 gallons on a hot summer day). c) They store food in winter. d) They guard against erosion.
NOTES: Aerial roots: These are above ground, such as ivy roots, to help the plant cling; orchids absorb water through theirs, and, in the swamplands, we find the `knees' of the Taxodium distichum, or Swamp Cypress, getting fresh air in its oxygen-poor habitat. (See 2 below.)
Helmont: Formerly, people thought that roots actually devoured the soil; to prove otherwise, 300 years ago, this Dutchman kept a willow for five years in a large pot, and found, to everyone's amazement, that the willow had gained 164 lbs. while the soil had lost 2 oz.! (See 3 below.)
Geotropic: Roots always go down; this tropism is known as 'geotropism.'
Mosses have no roots, their food being absorbed by their leaves.
Potatoes are underground stems and not roots.
Root warfare: Some Asteraceae have a toxic root excretion which may be an element of their success (Shasta daisies cause other flowers to wilt even when cut). Grass roots are toxic to apples, thus provoking them to fruit, a reason that orchards have grass. (See 4 below.)
Tamarisk: In digging for the Suez Canal, roots of this tree were found 30 meters underground! (See 5 below.)
NOTES Updated 2013 (RP):
1. Adventitious roots (fibrous roots) occur in the monocotyledonous group of plants that includes grasses, orchids, lilies. Taproots occur in gymnosperms (conifers, cycads) and in dicotyledonous plants (magnolias, hydrangeas, rhododendrons, clematis etc.)
2. There is little actual evidence for this common assertion; in fact, swamp-dwelling specimens whose knees are removed continue to thrive, and experiments have demonstrated that the knees are not effective at depleting oxygen in a sealed chamber.
3. Jean (Jan) Baptist van Helmont (1580 -1644) was a Flemish chemist, physiologist, and physician. He is remembered for his ideas on spontaneous generation, his willow tree experiment, and his introduction of the word 'gas' (from the Greek word chaos) into the vocabulary of scientists. He conducted an experiment, sometimes described as flawed in its design, on willow trees, but the results described by Erica are correct.
4. Allelopathy: inhibition of one species of plant by chemicals produced by another.