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. 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 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 close to a lamp, broad mites, and some calcium or boron problems show up first as twisted, stunted or dead growing tips, because that is where new tissue forms. When the newest growth looks 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.
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.
A dormant shoot bud in the angle (axil) between a leaf and the stem at each node, able to grow into a branch or a flower cluster.FIM is a training cut that pinches off most, but not all, of a plant's newest growing tip, often producing three or four new main shoots instead of one.Heat stress is damage or slowed growth when leaf or canopy temperature rises above what the plant can handle, typically above about 30–32 °C (86–90 °F) in cannabis.Polyphagotarsonemus latus, a microscopic tarsonemid mite whose toxic feeding twists, glazes and stunts new growth; often mistaken for calcium deficiency or heat stress.Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow.Bag appeal is how good flower looks in the bag or jar, frost, colour, density and trim, which sells cannabis but does not measure its quality.The dense, elongated cluster of flowers that forms at the end of a stem or branch; the main cola tops the leader.The suppression of side-shoot growth by the main growing tip, driven mainly by auxin flowing down the stem from the apex.The point on a stem where a leaf (petiole) and its axillary bud attach; branches, flowers and clone roots all originate at nodes.A class of plant hormones, chiefly indole-3-acetic acid (IAA), that drives cell elongation, apical dominance, bending toward light and root formation.
