The removal of phloem tissue leads to gradual death of a plant because phloem is essential for transporting sugars produced during photosynthesis from the leaves to the rest of the plant. Without this transport, the plant can't sustain its growth and development, ultimately leading to its demise.

Here's a breakdown of why:

* Photosynthesis: Plants produce sugars (mainly glucose) during photosynthesis in their leaves. These sugars are the primary source of energy for the plant.

* Phloem Function: Phloem tissue is a network of living cells that acts as a transport system for these sugars. It moves them from the leaves to other parts of the plant, including roots, stems, flowers, and fruits.

* Essential Functions: These sugars are crucial for:

* Growth: Providing energy for cell division and elongation, enabling the plant to grow.

* Maintenance: Supplying energy for essential functions like respiration, repair, and defense.

* Storage: Sugars are stored in roots, stems, and fruits for future use.

* Consequences of Phloem Removal: When phloem is removed, the transport of sugars is disrupted. The leaves continue to photosynthesize and produce sugars, but these sugars cannot reach the rest of the plant. Without a constant supply of energy, the plant's growth and essential functions are severely impaired.

* Gradual Death: The plant will first experience stunted growth and wilting. Eventually, it will be unable to maintain its essential functions, leading to a gradual decline and eventual death.

Note: The plant's death is gradual because other tissues may still have some stored sugars, allowing them to function for a period of time. However, the lack of fresh sugar transport from the leaves will ultimately cause the plant to succumb.