Comparisons related to Phloem

Comparison # 1
Vessels Sieve tubes
These have open ends. These have sieve plates at the ends.
Vessels are wider. These are narrow.
They have various types of thickenings. They have no such types of thickenings.
Vessels have thick, rigid, and lignified walls. These have thin, extensible, and cellulosic cell walls.
On maturity, they are dead. They are alive when they mature.
They are permeable for all compounds. They are semi-permeable.
Absorb water or air on cutting. Exude cell sap on cutting.
Have low sap concentration. Have high sap concentration.
Translocate both solutes and solvents. Translocate solute only.
Do not have turgor pressure. Turgid cells have high turgor pressure.
May partially collapse on functioning. Distended by pressure on functioning.
Translocation speed is up to 75 cm/mm. Translocation speed is up to 5 cm/mm.
Comparison # 2
Protophloem Meta phloem
The first phloem formed is the protophloem. After growth, the phloem differentiates and forms metaphloem.
It is found in an active and functional state in the young and actively growing parts of plants. It is present in mature parts of plants.
Sieve elements are thin and inconspicuous. Sieve elements are wide, long, and conspicuous.
Protoplasts are vacuolated and without nuclei. Protoplasts contain one or more nuclei. And disappear in mature sieve elements.
Companion cells may be present or absent. Companion cells are always present.
Elements of protophloem are short-lived. Metaphloem elements remain functional for a longer period.
Further Reading:  Conservation of Biodiversity - Types, & Methods of Conservation (In-situ, Ex-situ)
Comparison # 3
Primary Phloem Secondary Phloem
Derived from the procambium of apical meristem. Derived from the vascular cambium of the lateral meristem.
Protophloem and metaphloem elements are clearly demarcated. There is no differentiation in the proto and metaphloem of secondary phloem.
Sieve tubes are long and narrow. Sieve tubes are short and wide.
Phloem parenchyma is less developed and scanty. Parenchyma is well developed and abundant.
Sclereids are generally absent. Sclereids are present in secondary phloem.
Callus formation is absent or very little. Callus formation is abundant.
Primary medullary rays are formed from the activity of apical meristems. Secondary medullary rays are formed from the activity of initials of the cambium.
Medullary rays are homocellular. Medullary rays are homocellular or may be heterocellular.