Question

The nature of stele in primitive vascular plants was
1. Protostele
2. Siphonostele
3. Dictyostele
4. Atactostele

Answer 1

Correct Answer - Option 1 : Protostele

The correct answer is Protostele.

• The vascular cylinder of a stem or root is called the stele.
• The simplest and apparently most primitive type of stele is the protostele, in which the xylem is in the center of the stem, surrounded by a narrow band of phloem.
• It in turn is bounded by a pericycle of one or two cell layers and a single cell layer of endodermis.
• The stele consists solely of primary tissues differentiated from procambial strands derived from the apical meristem.
  • Secondary vascular tissue (wood consists of secondary xylem) is derived from vascular cambium.
• The stele functions in the transport of water, nutrients, and photosynthates.

• Siphonostele is a modification of protostele arrangement and it occurs in many ferns and some vascular plants.
  • The main characteristic feature of the siphonostele is the presence of a central pith surrounded by the vascular tissue.
  • Also, this type of arrangement has interruptions in the vascular strand where leaves originate. These interruptions are known as leaf gaps.
• Atactostele is a type of eustele, found in monocots, in which the vascular tissue in the stem exists as scattered bundles.