3 Comparisons related to Xylem

Comparison # 1
Tracheids Vessels


The tracheids are short generally up to 1mm in length and rarely go up to 12 cm. They are comparatively longer and may reach up to 10 cm. in rare cases, they go up to 2 – 6 meters.
Consists of a single elongated cell. The vessel consists of a row of cells placed one above the other.
They have tapering ends. They do not have tapering walls.
They are not tubular. They are tubular.
These are separated by cross walls and found one above the other. They have no cross walls.
They have bordered pits and are not perforated. These are may be perforated by small or large pores.
They are not adapted for the conduction of water. Vessels are well adapted for the conduction of water.
Found in all vascular plants. Found only in angiosperms.
Comparison # 2
Protoxylem Metaxylem
In these, vessels are formed earlier. In these, vessels are formed later.
It matures before the plant organs have completed their elongation. They mature after the elongation and growth if plant organs.
It has a narrow lumen. Its lumen is wider.
Possesses annular and spiral thickenings. Have scalariform, reticulate, and pitted types of thickenings.
Subjected to stress and strain. Not subjected to stress and strain.
Formed from procambium. Formed from fascicular and inter-fascicular cambium.
Do not have tyloses. It contains tyloses.
Protoxylem elements are less prominent. The elements of the metaxylem are much prominent.
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Comparison # 3
Primary Xylem Secondary Xylem
Formed by the activity of procambium of the apical meristem. Formed by the activity of vascular cambium of the lateral meristem.
Tracheids and vessels are narrow and long. Tracheids and vessels are wide and short.
Protoxylem and metaxylem are distinct in them. Protoxylem and metaxylem are not differentiated in it.
Primary medullary rays are formed by histogen of the apical meristem. Secondary medullary rays are formed by initials of the cambial ring.
Axial and radial systems are not distinct. Axial and radial systems are distinct.
Heartwood and sapwood are not distinct in them. Heartwood and sapwood are distinct in woody trees.
Xylem fibers are absent but if present; are in few numbers. Xylem fibers are found abundantly.
Annual rings are not formed. Annual rings are formed in woody plants.
Tyloses are not found in vessels. Vessels have tyloses.
The primary xylem maybe ends arch, mesarch, or exarch. There is no such differentiation in them.
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