# Apical meristem

> The zone of dividing cells at the very tip of a shoot (or root) that produces new leaves, nodes and stem; removing it is what topping does.

- Canonical: https://genetixbay.com/knowledge/glossary/apical-meristem.html
- Also written: shoot apical meristem, SAM, growing tip, growth tip, shoot tip
- Glossary category: Plant biology · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

An apical meristem is a small region of undifferentiated, actively dividing cells at the tip of a shoot or root. The shoot apical meristem builds the plant upward: it lays down each new node, leaf primordium and [axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md). The root apical meristem, protected by the root cap, drives root growth downward.

## In practice

Topping removes the shoot apical meristem of the main stem. With the tip gone, two axillary buds below take over, giving two main shoots. [FIM](https://genetixbay.com/knowledge/glossary/fim.md) removes most of the young tip but leaves some meristem tissue, which often produces three or more shoots, less predictably.

The meristem is fragile. [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md) close to a lamp, [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), and some calcium or [boron](https://genetixbay.com/knowledge/glossary/boron.md) problems show up first as twisted, stunted or dead growing tips, because that is where new tissue forms. When the newest growth [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) wrong, look at the tip first.

In flowering, the apical meristem of each shoot converts to producing flowers and forms the top of the [cola](https://genetixbay.com/knowledge/glossary/cola.md).

## Don't confuse with

- **Axillary bud**: a dormant meristem at a node, held back by the apex.
- **Apical dominance**: the control the tip exerts, not the tissue itself.
- **Cambium**: the lateral meristem that thickens stems.

## Related terms

[Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md), [Node](https://genetixbay.com/knowledge/glossary/node.md), [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md)

## Read more

- [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md)
- [FIM: pinching most of the tip for multiple tops](https://genetixbay.com/knowledge/training/fim.md)

## Sources

1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates.