Monocot and dicot Stems

Introduction

The vascular bundles are irregularly scattered in the monocot stem. Monocot stem lacks a clear distinction between the cortex and pith. In a monocot stem, the peripheral layers contain smaller bundles but they gradually become thicker and larger towards the centre. In some of the plants, the vascular bundles are formed out of one or more indistinct rings called the band of sclerenchyma. Monocot is identified by a V-shaped arrangement of xylem cells. The following table shows the major differences between monocot and the dicot stems.

Table of Contents

1. Introduction

2. Growth in a Stem

3. Types of Stems

   3.1  Underground stems

   3.2  Subaerial Stems

   3.3  Aerial Stems

 

 

Criteria

Dicot Stem

Monocot Stem

Arrangement  of Vascular Bundle

In dicot stems, the vascular bundles are arranged in the form of one or two broken rings.

In monocot stems, the vascular bundles are scattered across the stem without a definite arrangement.

Bundle Sheath

Absent in the dicot stems

The bundle sheath surrounds the scattered vascular bundles of a monocot stem.

Hypodermis

The hypodermis of the dicot stem is made up of the collenchyma.

The hypodermis in the monocot stem is made up of the sclerenchyma.

Presence or absence of Cortex  and  Stele

The vascular system in dicots contains 2 distinct regions, I,e, cortex, and stele.

The vascular bundles are scattered, and they lack the distinct cortex and stele.

 

Growth in a Stem

The growth of the stem is divided into, primary growth, and the secondary growth. Primary growth occurs at the apical tips of the stem. It occurs as a result of rapidly dividing merismatic tissues found in the stem. Secondary growth makes stem thicker by virtue of the growth of lateral meristems. Secondary growth is absent in the herbaceous plants as they lack cambium responsible for their secondary growth. In simple words, primary growth enhances the linear growth of plants but the secondary growth accelerates the thickness of stems.

 

Types of Stems

Based on the location of the stem stems are classified as the Underground stem, Aerial stem, and Subaerial stem 

Underground stems

The underground stems remain at the ground level but they produce aerial shoots that reach well above the level of the soil. Roots of an underground plant are present superficially. Stems of potato and onion help in the storage of food and perennation. They are also capable of vegetative propagation. Underground stems are further classified as Rhizome, tuber, bulb, and corm. Rhizome has a thick underground stem with distinct nodes and internodes ( Ginger). The tuber has a horizontal underground stem with their tips help in the accumulation of stored food (Potato). Bulb is a short underground stem present with a fleshy base and leafy scales. 

 Subaerial Stems

Subaerial Stems run parallel to the ground. They have nodes that turn into roots at some point. Sub-aerial stems are classified as a runner, offset, stolon, and sucker. Runner grows parallel to the ground with a creeping stem. Nodes on the lower side of the stem give out adventitious roots at regular intervals. A runner develops from the axils of lower leaves of the aerial stem. Offset type is shorter and thicker than the runner commonly found in aquatic plants. Stolon is similar to a runner that arises from the lower part of the main axis. Sucker stems are very similar to the stolon but they grow obliquely upwards resulting in the formation of a new plant. 

Aerial Stems

Aerial Stems are formed above the ground level. They are classified into thorns, tendril, phylloclade, cladode, and bulbil. Thorns are the modifications of a typical stem that looks hard, woody and sharp outgrowths (roses). Tendril has a slender, wavy, twining strands help in supporting the plant`s weight by encircling around tall trees. Phylloclade is a green, flattened or cylindrical stem looks like a leaf capable of conducting photosynthesis. Cladode is a modification of the phylloclade but they have additional internodes. Bulbil stems are actually the modified axillary buds. They look like fleshy and rounded as they store food in them.

 



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