Underground stems are modified plant structures that derive from stem tissue but exist under the soil surface. Plants have two axis of growth, which can be best seen from seed germination and growth. Seedlings develop two structures or axis of growth, one that develops up word out of the soil, called stems, and structures that develop downward which are called roots. The roots are modified to have root hairs and branch indiscriminately with cells that take in water and nutrients, while the stems are modified to move water and nutrients to and from the leaves and flowers. Stems have nodes with buds where leaves and flowers arise at specific locations, while roots do not. Plants use under ground stems to multiply there numbers by asexual reproduction and to survive from one year to the next, usually over a period of dormancy. Plants produce these modified stems so they can survive a cold or dry period which normally is a period of inactive growth, and when the cold or dry period is over the plants begin new growth from the underground stems. Being underground protects the stems from the elements during the dormancy period, such as freezing and thawing in winter or extreme heat and drought in summer or fire. They can also protect plants from heavy grazing pressure from animals, the plant might be eaten to the ground but new growth can occur from below ground that can not be reached by the herbivores. A number of weedy species use underground stems to spread and colonize large areas since the stems do not have to be supported or strong, less energy and resources are needed to produce these stems, often these weeds have more mass under ground than above ground.
In common parlance, a stem is any elongated, usually narrow, extension or supporting structure of an object. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Soil comprising the pedosphere is positioned at the interface of the lithosphere and biosphere with the atmosphere and hydrosphere. ... A ripe red jalapeño cut open to show the seeds For other uses, see Seed (disambiguation). ... Roots is: The plural of Root Roots (album) Roots (TV miniseries), a mini-series based on a novel by Alex Haley Roots: The Saga of an American Family, a novel by Alex Haley Roots Canada Ltd. ... Flower buds have not yet bloomed into a full-size flower. ... This article is about human asexuality; asexual reproduction is a separate topic. ... Dormancy is a arrested plant growth. ... Grazing To feed on growing herbage, attached algae, or phytoplankton. ... A deer and two fawns feeding on some foliage A herbivore is often defined as any organism that eats only plants[1]. By that definition, many fungi, some bacteria, many animals, about 1% of flowering plants and some protists can be considered herbivores. ...

Types of underground stems

Different forms of underground stems include:

• Bulb - Short, upright organ used by plants for food storage or reproduction, with specialized leaves modified into thick flesh scales. Tulips and Lilies.
• Corm - Short, upright, hard or fleshy stems covered with thin, dry papery leaves.
• Rhizome - With reduced scale like leaves. The top can generate leafy stems while the bottom can produce roots. Iris.
• Stolon - Horizontal stems that run at or just below the soil surface with nodes that root and long internodes, the ends produce new plants. When above ground they are called runners.
• Tuber - An enlarged fleshy end of a stem, generally from rhizomes but often also referring to thickened roots too.