The key difference between hydroids and leptoids is that hydroids are specialized cells that conduct water in bryophytes and are analogous to tracheids in vascular plants, while leptoids are specialized cells that transport sugar in bryophytes and are analogous to sieve elements in vascular plants.
Bryophytes are a group of non-vascular plants. In fact, they are primitive plants that lack true stem, roots and leaves. They don’t have xylem or phloem. However, some mosses, mosses especially in the moss subclass Polytrichidae, have specialized cells to conduct water, minerals and sugar. Hydroids are specialized cells that transport water and minerals in some mosses. They are analogous to tracheids in vascular plants. Leptoids are another type of specialized cells that transport sugar and other nutrients in bryophytes. Moreover, they are analogous to sieve elements of vascular plants.
CONTENTS
1. Overview and Key Difference
2. What are Hydroids
3. What are Leptoids
4. Similarities Between Hydroids and Leptoids
5. Side by Side Comparison – Hydroids vs Leptoids in Tabular Form
6. Summary
What are Hydroids?
Hydroids are specialized cells found in certain mosses that transport water and minerals drawn from the soil. These cells are analogous to tracheids in vascular plants. However, unlike tracheids, they don’t have lignin in their cell walls. They are elongated cells that have overlapping end walls. Moreover, they have pores in their thin cell walls. Generally, hydroids don’t have secondary thickening in their cell walls. They become dead and empty at maturity. Hydroids are found in the gametophytic phase of a plant life cycle and in the seta in the sporophytic phase.
Figure 01: Hydroids (A) and Leptoids (B) in Moss Stem Cross Section
What are Leptoids?
Leptoids are a type of vascular cells that are specialized to transport sugar in some mosses. Therefore, they are analogous to sieve elements in vascular plants. Similar to hydroids, leptoids are also elongated cells that have overlapping end walls. Leptoids contain callose. They surround hydroids, forming a layer around them. Leptoids are living cells, even at maturity. However, their nuclei degenerate at maturity. These cells are found in the gametophytic phase of a plant life cycle and in the seta in the sporophytic phase.
What are the Similarities Between Hydroids and Leptoids?
- Hydroids and leptoids are two types of vascular cells found in certain mosses.
- They are analogous to vascular tissues in vascular plants.
- But they lack lignin, unlike vascular tissues.
- They occur in the gametophytic phase of a plant life cycle and in the seta in the sporophytic phase.
- Both hydroids and leptoids are elongated cells.
- They have overlapping end walls.
- Both types of cells have pores in their cell walls.
What is the Difference Between Hydroids and Leptoids?
Hydroids and leptoids are elongated cells that act as vascular cells in certain mosses. Hydroids are water and mineral conducting specialized cells, while leptoids are sugar-conducting specialized cells. So, this is the key difference between hydroids and leptoids.
Moreover, hydroids are analogous to tracheids in vascular plants, while leptoids are analogous to sieve tubes in vascular plants. Therefore, this is another significant difference between hydroids and leptoids. Furthermore, hydroids are the innermost cells found in the moss stem while leptoids make a layer surrounding the hydroids in the moss stem.
Below infographic summarizes the difference between hydroids and leptoids.
Summary – Hydroids vs Leptoids
Generally, bryophytes lack vascular tissues and strengthening tissues. But, some mosses have two types of vascular cells as hydroids and leptoids. Hydroids transport water and minerals in these mosses, while leptoids transport sucrose in some mosses. Therefore, hydroids are analogous to tracheids in vascular plants, while leptoids are analogous to sieve elements in vascular plants. So, this is the summary of the difference between hydroids and leptoids.
Reference:
1. “Hydroid (Botany).” Wikipedia, Wikimedia Foundation, 4 Feb. 2020, Available here.
2. “Leptoid.” Wikipedia, Wikimedia Foundation, 10 July 2018, Available here.
Image Courtesy:
1. “Moss stem enlarged L” By Jon Houseman – Jon Houseman and Matthew Ford (CC BY-SA 4.0) via Commons Wikimedia