How plants grow

By iMages - November 12, 2020

How, exactly, do roots and stems grow? 

The primary growth process of all living things is cell division, or mitosis. 

Cell division takes place within the specialized growth tissue of a plant, called meristematic tissue or meristem. 

Primary growth occurs in the apical meristem, located at the tip of a root or stem. 

In addition, plants have axillary meristem in discrete spots along the length of their roots and stems, where branching or budding can occur. 

Growth tissue distributed along the entire length of each root or stem is called lateral meristem. It contributes to the thickening of the root or stem to provide strength and support, turning twigs into branches and branches into boughs.

Gardener’s Glossary

All plants either develop woody stems or stay herbaceous, with pliable stems. Trees and shrubs produce herbaceous shoots in the spring that transform into woody stems. Woody plants are also perennials, which means they live more than two years, sometimes for centuries. Herbaceous plants don’t form woody stems but can be annuals, biennials, or tender or hardy perennials.

Annuals are single-season plants that are genetically programmed to germinate, grow, flower, fruit, and die in a single season, sometimes sooner. Many crop plants and common weeds are annuals.

Biennials are plants that require two years to reach maturity. The first year they germinate and grow, making plenty of stems and leaves but no flowers, fruit, or seeds. Come winter they die down to the ground, but the roots survive so they can spring up again next season. During the second year, biennials make flowers and set seed. Thereafter the plant dies and disappears, its only vestiges some random seedlings that pop up nearby the following spring.

Tender perennials are genetic perennials but last only one year when grown in climates with winters that get too cold for them. These include many fast-growing flowers typically planted in beds for temporary seasonal displays (known as bedding plants), like impatiens, petunias, geraniums, and marigolds. The closer you live to the equator, the more likely these plants will be to last more than one season in your garden.

Hardy perennials come back year after year. Their tops may die back during the winter, but their roots remain alive so they resprout in the spring. Perennials can be woody, semiwoody, or herbaceous.

Mitosis requires sun energy, water, and nutrients to fuel cell division. 

In the absence of adequate sunlight, a measure that varies from plant to plant, plants resort to another growth process called elongation. 

Cell walls swell with water, soften, and expand. The threads of cellulose within the cell wall loosen and spread so that the cells bulge on two sides. 

When the pressure is relieved, the cells slim back and elongate lengthwise.

Cell elongation results in leggy plants with weak stems and explains why plants on a windowsill reach toward the sun. 

The meristematic tissue exposed to sunlight has enough energy for mitosis, resulting in regular-size, sturdy cells. 

Meristem with insufficient sun exposure doesn’t have enough energy to divide, so the cells resort to elongation and that side of the stem grows longer than the other, causing the stem to bend toward the sunlight.




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