In dicotyledon the vascular bundles are usually more or less in a ring and show different arrangements at the nodes and internodes.
The vascular cylinders are generally continuous at the internode and their continuity is interrupted at the nodal region due to the emergence of bundles that terminate either at the leaf bases, axillary buds or stipules etc.
A leaf gap may be a space within the stem of a plant through which the leaf grows.
The leaf is connected to the stem by the leaf trace, which grows through the leaf gap.
This type of node exhibits one leaf trace to a leaf and therefore the leaf trace is related to one lacuna.
- Unilacunar nodes are stipulate.
- Eg: Hibiscus
This type of nodes has two leaf traces to a single leaf and one lacuna.
The two leaf traces are associated with the single lacuna.
- Dilacunar nodes are stipulate.
- Eg: Ixora
This type of nodes has three leaf traces to a leaf and three lacuna.
Each trace is associated with single lacuna.
Among the three traces, the trace that occurs in the median position with reference to leaf is referred to as median trace.
The other are called lateral traces.
- This type of nodes has exstipulate.
- Eg: Nerium