Question

In a dicotyledonous stem, the sequence of tissues from the outside to the inside is
A. Phellem- Pericycle - Endodermis - Phloem
B. Phellem - Phloem- Endodermis - Pericycle
C. Phellem - Endodermis - Pericycle - Phloem
D. Pericycle - Phloem - Endodermis - Phloem

Answer 1

Hint:The inner structure of a dicot stem consists mainly of epidermis, hypodermis, endodermis, pericycle, vascular bundle and pith.

Complete answer:
Dicot stems have a well-developed epidermis, a dermis layer with multicellular stem hair. The inner structure of a dicot stem consists mainly of epidermis, hypodermis, endodermis, pericycle, vascular bundle and pith. Examples of dicot stem are sunflower and Cucurbita.
The cross section of a typical young dicotyledonous stem indicates the epidermis is the ultimate defensive layer. It may have trichomes and a few stomata and coated with a thin layer of cuticle. The cortex is composed of cells divided into many layers between epidermis and pericycle. There are three subzones. A few layers of collenchymatous cells below the epidermis are produced in the outer hypodermis. Cortical layers under hypodermis are rounded parenchymatous, thin wall cells that have visible intercellular spaces. Endodermis is the innermost layer of the cortex. Pericycles are in the shape of semiLunar patches of sclerenchymatous cells on the inner side of the endodermis and above the phloem. There are several layers of parenchymatous cells in the vascular bundles, which are medullary rays. A broad variety of vascular bundles is arranged in a circle, which is typical of a dicot stem. The pith is constituted by a large number of rounded, parenchymatous cells with great intercellular spaces in the middle part.

Thus, the correct answer is option C. i.e., Phellem - Endodermis - Pericycle - Phloem.

Note:Phellem is the outermost suberized cells which are commonly known as cork cells. Phellem save the plants from excessive evaporation, fluctuate temperature, ingestion by animals, etc.