Q.How can you differentiate between free central and axile placentation?

Both free central and axile placentation involve ovules attached to a placenta running through the middle of the ovary, but they differ in the internal structure of the ovary itself. In axile placentation, the ovary is divided into several chambers by septa, and the ovules are attached to a central, axial placenta running through these locules, as seen in china rose, tomato and lemon. In free central placentation, by contrast, the septa are entirely absent, so the ovary remains a single chamber, and the ovules are borne directly on a central axis rising within that undivided cavity, as seen in Dianthus and Primrose.

• Axile: multilocular ovary (septa present), ovules on a central axis within the chambers …

Placentation describes how ovules are arranged within the ovary, and both these two types share the feature of a central placental axis, which is why they can be confused at first glance.

• In axile placentation, the placenta is axial in position, and the ovules attach to it inside an ovary that is divided into multiple chambers, or locules, by internal partitions called septa. China rose, tomato and lemon are given as examples of this pattern.
• In free central placentation, the ovules are likewise borne on a central axis, but crucially the septa that would otherwise divide the ovary into chambers are absent altogether, leaving a single, undivided cavity with the ovule-bearing axis rising freely within it. Dianthus and Primrose are given as examples of this pattern. …

Method: The "Check for Walls" Test

Free central and axile placentation are easy to confuse because both place ovules on a central axis, so the fast, reliable test is to check for exactly one feature that differs between them, the presence of septa, dividing walls.

The test, in one question: if this ovary were cut across, would the cavity appear divided into separate wedge-shaped chambers by walls, or would it be one single open space?

If walls are present, with multiple chambers, locules, this is axile placentation. The central axis where the fused carpel walls meet is what carries the ovules, and because true septa exist, the ovary is described as multilocular. Examples: china rose, tomato, lemon, cut a tomato and distinct wedge-shaped compartments appear, each with seeds attached at the central meeting point.

If no walls are present at all, one open chamber, this is free central placentation. The ovules still sit on a central column, but that column stands free, nothing divides the cavity around it into separate compartments. Examples: Dianthus, Primrose. …