Introduction:
Plants are complex organisms made up of various tissues that perform different functions. While it is true that a significant portion of plant tissues are composed of dead cells, it is important to understand the reasons behind this phenomenon.

Reasoning:
Mechanical Strength:
- The sedentary lifestyle of plants necessitates the need for mechanical support to withstand various environmental conditions such as wind, rain, and gravity.
- Dead cells, unlike living cells, have rigid cell walls composed of cellulose, a complex carbohydrate that provides structural support to the plant.
- These dead cells make up the majority of the plant's structural tissues, including the stem, trunk, and branches, and help maintain the plant's overall shape and stability.

Less Maintenance:
- Dead cells do not require energy or resources for their maintenance and repair, unlike living cells that constantly undergo metabolic processes.
- Living cells need to expend energy on activities such as growth, reproduction, and repair, which would be inefficient for structural tissues.
- By having most of its structural tissues composed of dead cells, plants can allocate more resources towards other vital functions such as photosynthesis and nutrient uptake.

Exceptions:
- While most of the plant tissues are indeed dead, there are exceptions such as actively growing plant parts like roots, leaves, and reproductive structures.
- These regions contain living cells that are responsible for growth, photosynthesis, and reproduction.
- Additionally, some specialized tissues, like the phloem and xylem, which transport nutrients and water throughout the plant, contain both living and dead cells.

Conclusion:
In conclusion, the assertion that most plant tissues are dead is valid due to the sedentary nature of plants and the need for mechanical strength. Dead cells provide the necessary structural support without requiring maintenance, allowing plants to allocate resources towards other essential functions. However, it is important to recognize that living cells also play crucial roles in specific plant tissues, such as growth and reproduction.