Q.A student was observing a slide with no label. The section had some vascular bundles scattered in the ground tissue. It is section of a monocot stem! He exclaimed. No! it is section of fern rachis, said the teacher. Teacher told to observe vascular bundle again. Student agreed, Why?

Step 1. At first glance, both a fern rachis and a monocot stem can show multiple vascular bundles that appear scattered through the ground tissue, which is why the student's first guess (monocot stem) was reasonable.

Step 2. But 'scattered-looking' is not the same as anatomically identical — the teacher's instruction to look again at the internal structure of each bundle points to the real distinguishing feature.

Step 3. A true monocot stem's bundles are conjoint, collateral and closed (xylem and phloem side by side on the same radius, no cambium), each individually wrapped in its own sclerenchymatous bundle sheath, embedded in ordinary parenchymatous ground tissue. …

Distinguish 'scattered-looking bundles' at low magnification from the actual xylem-phloem arrangement …

• Diagnosing a section from its bundles' overall distribution alone, without checking the internal (conjoint-collateral vs concentric) arrangement of each individual …