Biology · Anatomy of Flowering Plants · NEET
In a ring. A dicot stem has a large number of vascular bundles arranged in one ring around the pith. This ring is the classic sign of a dicot stem. A monocot stem is the opposite: its bundles are scattered all through the ground tissue. NEET often gives a T.S. description and asks you to name the organ, so 'ring = dicot stem, scattered = monocot stem' is a fast rule.
It is open. 'Open' means cambium is present between the xylem and phloem. Because cambium can divide, it forms secondary xylem and secondary phloem, so the stem can undergo secondary growth (increase in girth). A monocot stem has no cambium in its bundles, so those bundles are 'closed' and cannot grow in thickness. Remember: open = has cambium = can do secondary growth.
The starch sheath is the endodermis of the dicot stem. It is the innermost layer of the cortex, and its cells are rich in starch grains, so it is also called the starch sheath. NEET has matched 'starch sheath' to 'endodermal cells rich in starch' in a matching question, so link starch sheath = endodermis of dicot stem.
Endarch. In a dicot stem each vascular bundle has endarch protoxylem, which means the protoxylem (first-formed xylem) lies toward the centre and the metaxylem lies toward the outside. This is the stem pattern. Roots are the opposite (exarch), where protoxylem lies toward the periphery. So: stem = endarch, root = exarch.
Medullary rays are the few layers of radially placed parenchyma cells that lie between the vascular bundles. Because the bundles sit in a ring, the parenchyma strips running between them, from the pith outward, are the medullary (pith) rays. They connect the pith and the cortex and later help in the sideways transport of food and water.
From outside inward: epidermis (with cuticle, sometimes trichomes and a few stomata), then cortex in three zones (collenchymatous hypodermis, parenchymatous general cortex, and the endodermis or starch sheath as the innermost cortex layer), then pericycle (semi-lunar sclerenchyma patches above the phloem), then the ring of vascular bundles with medullary rays between them, and finally the parenchymatous pith in the centre.
The transverse section of a plant shows: (a) large number of scattered vascular bundles surrounded by bundle sheath, (b) large conspicuous parenchymatous ground tissue, (c) vascular bundles conjoint and closed, (d) phloem parenchyma absent. Identify the plant material:
Find the statement that is NOT correct with regard to the structure of monocot stem.
Match List-I with List-II. A. Conjunctive tissue B. Casparian strips C. Subsidiary cells D. Starch sheath (I) Specialised cells near guard cells (II) Endodermal cells rich in starch (III) Tissue between xylem and phloem (IV) Endodermal cells with suberin deposition
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Because NEET tests dicot vs monocot stem almost every year, and the ring is the single most reliable clue. Ring of bundles = dicot stem; scattered bundles = monocot stem. If you remember only one dicot-stem fact, remember the ring.
Yes. The centre of a dicot stem is filled with parenchymatous pith with large intercellular spaces. In a monocot stem there is no separate pith; instead there is one large, undifferentiated parenchymatous ground tissue. So a well-marked pith supports 'dicot stem.'
The vascular bundle is conjoint (xylem and phloem on the same radius) with endarch protoxylem (protoxylem toward the centre). Conjoint and endarch are stem features; radial and exarch belong to roots.
In a dicot stem the hypodermis is collenchymatous (living, gives mechanical strength to the young stem). In a monocot stem the hypodermis is sclerenchymatous. NEET 2025 used this exact swap as a trap.
Yes. Because the bundles are open (cambium present), the vascular cambium can form secondary xylem and phloem, increasing the stem's girth. Monocot stems normally cannot, as their bundles are closed.
