Meristematic tissue is plant tissue whose cells keep the ability to divide by mitosis. Its cells are small, thin-walled, densely filled with cytoplasm and have little or no vacuole. Because these cells divide again and again, meristematic tissue is the source of all new cells and therefore the basis of plant growth. Unlike most animals, many plants keep growing throughout their lives because meristems remain active.
Position of meristems
Meristematic tissue is classified by where it is found:
- Apical meristem — at the tips of roots and shoots. Its division makes the root and shoot grow longer. This lengthening is called primary growth.
- Lateral meristem — arranged in cylinders along the sides of stems and roots (for example the cambium). Its division makes the stem and root grow wider/thicker. This thickening is called secondary growth.
Key idea
Apical meristem → growth in length. Lateral meristem → growth in girth (thickness).
How growth happens
Growth in plants involves three overlapping steps:
- Cell division — meristematic cells divide by mitosis to increase cell number.
- Cell enlargement — the new cells take in water, the vacuole swells, and the cells become longer. This is often the largest contribution to increased size.
- Cell differentiation — enlarged cells specialise into permanent tissues such as xylem, phloem or epidermis.
Example
At the tip of a growing root, the apical meristem divides. Just behind it the new cells lengthen in the zone of elongation, pushing the root tip deeper into the soil. Further back, the cells differentiate and root hairs form.
Why it matters
Because meristematic tissue is retained, a plant can repair damage, grow new branches and thicken its trunk year after year. The activity of lateral meristem is what produces wood and the annual rings seen in tree trunks. Understanding meristems also explains why cuttings and grafts can grow — they contain living dividing cells.
Remember
Meristem cells have little or no vacuole and dense cytoplasm — the opposite of a mature parenchyma cell with its large central vacuole.