Plant roots

Overview

The root is typically the part of the plant that grows into the soil, although it can be aerial in waterlogged soil. Roots have two main functions, anchoring the plant to the ground, and absorbing nutrients, water, and minerals for the plant. There are typically two types of roots, tap roots and fibrous roots, which will be explained on this page. Plant root systems can be very extensive, and are harder to study than the above ground biomass. Current methods for studying root systems include: the harvest method, isotopic analysis, root ingrowth, and rhizotrons. Roots can often have symbiotic relationships with mycorrhizal fungi.

Parts of the plant root

The root hairs are thin hairlike structures growing from the epidermis. These help with the absorption of moisture and nutrients from the soil, which is then transported to the rest of the plant. The majority of plant water absorption happens with the root hairs. The length and shape allows them to have a large surface area while being able to go between soil particles, both of which helps with water absorption. In legume plants, they are involved in root nodule formation.  
Xylem
Phloem
Pericycle
Endodermis
Apical meristem
Root cap

Citations

Gyssels, G., et al. “Impact of Plant Roots on the Resistance of Soils to Erosion by Water: a Review.” Progress in Physical Geography, vol. 29, no. 2, 2005, pp. 189–217.
Cannon, William Austin. “A Tentative Classification of Root Systems.” Ecology, vol. 30, no. 4, 1 Oct. 1949, pp. 542–548. 
http://www.justscience.in/articles/structure-and-function-of-plant-roots/2017/07/01
Glinski, J. Soil Physical Conditions and Plant Roots. CRC Press, 2018.
Russell, Robert Scott. Plant Root Systems: Their Function and Interaction with the Soil. English Language Book Society and McGraw-Hill, 1982.
Esau, K. 1965. Plant Anatomy, 2nd Edition. John Wiley & Sons. 767 pp.